diff --git a/src/Microsoft.OpenApi/Models/OpenApiDocument.cs b/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
index 7820a6f8e..3504a92f7 100644
--- a/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
+++ b/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
@@ -76,10 +76,27 @@ public void RegisterComponents()
         public IList<OpenApiSecurityRequirement>? SecurityRequirements { get; set; } =
             new List<OpenApiSecurityRequirement>();
 
+        private HashSet<OpenApiTag>? _tags;
         /// <summary>
         /// A list of tags used by the specification with additional metadata.
         /// </summary>
-        public IList<OpenApiTag>? Tags { get; set; } = new List<OpenApiTag>();
+        public ISet<OpenApiTag>? Tags 
+        { 
+            get
+            {
+                return _tags;
+            }
+            set
+            {
+                if (value is null)
+                {
+                    return;
+                }
+                _tags = value is HashSet<OpenApiTag> tags && tags.Comparer is OpenApiTagComparer ?
+                        tags :
+                        new HashSet<OpenApiTag>(value, OpenApiTagComparer.Instance);
+            }
+        }
 
         /// <summary>
         /// Additional external documentation.
@@ -123,7 +140,7 @@ public OpenApiDocument(OpenApiDocument? document)
             Webhooks = document?.Webhooks != null ? new Dictionary<string, IOpenApiPathItem>(document.Webhooks) : null;
             Components = document?.Components != null ? new(document?.Components) : null;
             SecurityRequirements = document?.SecurityRequirements != null ? new List<OpenApiSecurityRequirement>(document.SecurityRequirements) : null;
-            Tags = document?.Tags != null ? new List<OpenApiTag>(document.Tags) : null;
+            Tags = document?.Tags != null ? new HashSet<OpenApiTag>(document.Tags, OpenApiTagComparer.Instance) : null;
             ExternalDocs = document?.ExternalDocs != null ? new(document?.ExternalDocs) : null;
             Extensions = document?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(document.Extensions) : null;
             Annotations = document?.Annotations != null ? new Dictionary<string, object>(document.Annotations) : null;
diff --git a/src/Microsoft.OpenApi/Models/OpenApiOperation.cs b/src/Microsoft.OpenApi/Models/OpenApiOperation.cs
index 3acbd05ab..1e10f640c 100644
--- a/src/Microsoft.OpenApi/Models/OpenApiOperation.cs
+++ b/src/Microsoft.OpenApi/Models/OpenApiOperation.cs
@@ -23,11 +23,28 @@ public class OpenApiOperation : IOpenApiSerializable, IOpenApiExtensible, IOpenA
         /// </summary>
         public const bool DeprecatedDefault = false;
 
+        private HashSet<OpenApiTagReference>? _tags;
         /// <summary>
         /// A list of tags for API documentation control.
         /// Tags can be used for logical grouping of operations by resources or any other qualifier.
         /// </summary>
-        public IList<OpenApiTagReference>? Tags { get; set; } = [];
+        public ISet<OpenApiTagReference>? Tags 
+        { 
+            get
+            {
+                return _tags;
+            }
+            set
+            {
+                if (value is null)
+                {
+                    return;
+                }
+                _tags = value is HashSet<OpenApiTagReference> tags && tags.Comparer is OpenApiTagComparer ?
+                        tags :
+                        new HashSet<OpenApiTagReference>(value, OpenApiTagComparer.Instance);
+            }
+        }
 
         /// <summary>
         /// A short summary of what the operation does.
@@ -123,7 +140,7 @@ public OpenApiOperation() { }
         public OpenApiOperation(OpenApiOperation operation)
         {
             Utils.CheckArgumentNull(operation);
-            Tags = operation.Tags != null ? new List<OpenApiTagReference>(operation.Tags) : null;
+            Tags = operation.Tags != null ? new HashSet<OpenApiTagReference>(operation.Tags) : null;
             Summary = operation.Summary ?? Summary;
             Description = operation.Description ?? Description;
             ExternalDocs = operation.ExternalDocs != null ? new(operation.ExternalDocs) : null;
diff --git a/src/Microsoft.OpenApi/Models/References/OpenApiTagReference.cs b/src/Microsoft.OpenApi/Models/References/OpenApiTagReference.cs
index 6f218fc13..019d4c367 100644
--- a/src/Microsoft.OpenApi/Models/References/OpenApiTagReference.cs
+++ b/src/Microsoft.OpenApi/Models/References/OpenApiTagReference.cs
@@ -21,7 +21,7 @@ public override OpenApiTag Target
         {
             get
             {
-                return Reference.HostDocument?.Tags.FirstOrDefault(t => StringComparer.Ordinal.Equals(t.Name, Reference.Id));
+                return Reference.HostDocument?.Tags?.FirstOrDefault(t => OpenApiTagComparer.StringComparer.Equals(t.Name, Reference.Id));
             }
         }
 
diff --git a/src/Microsoft.OpenApi/OpenApiTagComparer.cs b/src/Microsoft.OpenApi/OpenApiTagComparer.cs
new file mode 100644
index 000000000..6652dd5ba
--- /dev/null
+++ b/src/Microsoft.OpenApi/OpenApiTagComparer.cs
@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.OpenApi.Models.Interfaces;
+
+namespace Microsoft.OpenApi;
+
+#nullable enable
+/// <summary>
+/// This comparer is used to maintain a globally unique list of tags encountered
+/// in a particular OpenAPI document.
+/// </summary>
+internal sealed class OpenApiTagComparer : IEqualityComparer<IOpenApiTag>
+{
+    private static readonly Lazy<OpenApiTagComparer> _lazyInstance = new(() => new OpenApiTagComparer());
+    /// <summary>
+    /// Default instance for the comparer.
+    /// </summary>
+    internal static OpenApiTagComparer Instance { get => _lazyInstance.Value; }
+
+    /// <inheritdoc/>
+    public bool Equals(IOpenApiTag? x, IOpenApiTag? y)
+    {
+        if (x is null && y is null)
+        {
+            return true;
+        }
+        if (x is null || y is null)
+        {
+            return false;
+        }
+        if (ReferenceEquals(x, y))
+        {
+            return true;
+        }
+        return StringComparer.Equals(x.Name, y.Name);
+    }
+
+    // Tag comparisons are case-sensitive by default. Although the OpenAPI specification
+    // only outlines case sensitivity for property names, we extend this principle to
+    // property values for tag names as well.
+    // See https://spec.openapis.org/oas/v3.1.0#format.
+    internal static readonly StringComparer StringComparer = StringComparer.Ordinal;
+
+    /// <inheritdoc/>
+    public int GetHashCode(IOpenApiTag obj) => string.IsNullOrEmpty(obj?.Name) ? 0 : StringComparer.GetHashCode(obj!.Name);
+}
+#nullable restore
diff --git a/src/Microsoft.OpenApi/Reader/V2/OpenApiDocumentDeserializer.cs b/src/Microsoft.OpenApi/Reader/V2/OpenApiDocumentDeserializer.cs
index 0aa2b8093..7e13578f3 100644
--- a/src/Microsoft.OpenApi/Reader/V2/OpenApiDocumentDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V2/OpenApiDocumentDeserializer.cs
@@ -104,7 +104,7 @@ internal static partial class OpenApiV2Deserializer
                 }
             },
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o)},
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)}
         };
 
diff --git a/src/Microsoft.OpenApi/Reader/V2/OpenApiOperationDeserializer.cs b/src/Microsoft.OpenApi/Reader/V2/OpenApiOperationDeserializer.cs
index 37c95c9b2..c2f6ca204 100644
--- a/src/Microsoft.OpenApi/Reader/V2/OpenApiOperationDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V2/OpenApiOperationDeserializer.cs
@@ -23,10 +23,12 @@ internal static partial class OpenApiV2Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(
-                                valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary",
diff --git a/src/Microsoft.OpenApi/Reader/V3/OpenApiDocumentDeserializer.cs b/src/Microsoft.OpenApi/Reader/V3/OpenApiDocumentDeserializer.cs
index c07d28d46..f6ca536c4 100644
--- a/src/Microsoft.OpenApi/Reader/V3/OpenApiDocumentDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V3/OpenApiDocumentDeserializer.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Reader.ParseNodes;
@@ -26,7 +27,7 @@ internal static partial class OpenApiV3Deserializer
             {"servers", (o, n, _) => o.Servers = n.CreateList(LoadServer, o)},
             {"paths", (o, n, _) => o.Paths = LoadPaths(n, o)},
             {"components", (o, n, _) => o.Components = LoadComponents(n, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o) },
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)},
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)}
         };
diff --git a/src/Microsoft.OpenApi/Reader/V3/OpenApiOperationDeserializer.cs b/src/Microsoft.OpenApi/Reader/V3/OpenApiOperationDeserializer.cs
index e9712da98..9fca4d14b 100644
--- a/src/Microsoft.OpenApi/Reader/V3/OpenApiOperationDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V3/OpenApiOperationDeserializer.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
@@ -19,10 +20,12 @@ internal static partial class OpenApiV3Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(
-                                valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary",
diff --git a/src/Microsoft.OpenApi/Reader/V31/OpenApiDocumentDeserializer.cs b/src/Microsoft.OpenApi/Reader/V31/OpenApiDocumentDeserializer.cs
index 4f3a05fcc..f16ac31cc 100644
--- a/src/Microsoft.OpenApi/Reader/V31/OpenApiDocumentDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V31/OpenApiDocumentDeserializer.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Reader.ParseNodes;
@@ -24,7 +25,7 @@ internal static partial class OpenApiV31Deserializer
             {"paths", (o, n, _) => o.Paths = LoadPaths(n, o)},
             {"webhooks", (o, n, _) => o.Webhooks = n.CreateMap(LoadPathItem, o)},
             {"components", (o, n, _) => o.Components = LoadComponents(n, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o) },
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)},
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)}
         };
diff --git a/src/Microsoft.OpenApi/Reader/V31/OpenApiOperationDeserializer.cs b/src/Microsoft.OpenApi/Reader/V31/OpenApiOperationDeserializer.cs
index cb44bb438..d969cca36 100644
--- a/src/Microsoft.OpenApi/Reader/V31/OpenApiOperationDeserializer.cs
+++ b/src/Microsoft.OpenApi/Reader/V31/OpenApiOperationDeserializer.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
@@ -16,9 +17,12 @@ internal static partial class OpenApiV31Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary", (o, n, _) =>
diff --git a/src/Microsoft.OpenApi/Services/OpenApiFilterService.cs b/src/Microsoft.OpenApi/Services/OpenApiFilterService.cs
index 20fa54839..5f439fe94 100644
--- a/src/Microsoft.OpenApi/Services/OpenApiFilterService.cs
+++ b/src/Microsoft.OpenApi/Services/OpenApiFilterService.cs
@@ -363,11 +363,11 @@ private static void ValidateFilters(IDictionary<string, List<string>> requestUrl
             if (tagsArray.Length == 1)
             {
                 var regex = new Regex(tagsArray[0]);
-                return (_, _, operation) => operation.Tags.Any(tag => regex.IsMatch(tag.Name));
+                return (_, _, operation) => operation.Tags?.Any(tag => regex.IsMatch(tag.Name)) ?? false;
             }
             else
             {
-                return (_, _, operation) => operation.Tags.Any(tag => tagsArray.Contains(tag.Name));
+                return (_, _, operation) => operation.Tags?.Any(tag => tagsArray.Contains(tag.Name)) ?? false;
             }
         }
 
diff --git a/src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs b/src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs
index 254528b41..e4420c3c3 100644
--- a/src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs
+++ b/src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs
@@ -309,14 +309,14 @@ public virtual void Visit(IOpenApiExample example)
         /// <summary>
         /// Visits list of <see cref="OpenApiTag"/>
         /// </summary>
-        public virtual void Visit(IList<OpenApiTag> openApiTags)
+        public virtual void Visit(ISet<OpenApiTag> openApiTags)
         {
         }
 
         /// <summary>
         /// Visits list of <see cref="OpenApiTagReference"/>
         /// </summary>
-        public virtual void Visit(IList<OpenApiTagReference> openApiTags)
+        public virtual void Visit(ISet<OpenApiTagReference> openApiTags)
         {
         }
 
diff --git a/src/Microsoft.OpenApi/Services/OpenApiWalker.cs b/src/Microsoft.OpenApi/Services/OpenApiWalker.cs
index ae4430067..68e3133d6 100644
--- a/src/Microsoft.OpenApi/Services/OpenApiWalker.cs
+++ b/src/Microsoft.OpenApi/Services/OpenApiWalker.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text.Json.Nodes;
 using Microsoft.OpenApi.Any;
 using Microsoft.OpenApi.Extensions;
@@ -60,7 +61,7 @@ public void Walk(OpenApiDocument doc)
         /// <summary>
         /// Visits list of <see cref="OpenApiTag"/> and child objects
         /// </summary>
-        internal void Walk(IList<OpenApiTag> tags)
+        internal void Walk(ISet<OpenApiTag> tags)
         {
             if (tags == null)
             {
@@ -72,9 +73,10 @@ internal void Walk(IList<OpenApiTag> tags)
             // Visit tags
             if (tags != null)
             {
-                for (var i = 0; i < tags.Count; i++)
+                var tagsAsArray = tags.ToArray();
+                for (var i = 0; i < tagsAsArray.Length; i++)
                 {
-                    Walk(i.ToString(), () => Walk(tags[i]));
+                    Walk(i.ToString(), () => Walk(tagsAsArray[i]));
                 }
             }
         }
@@ -82,7 +84,7 @@ internal void Walk(IList<OpenApiTag> tags)
         /// <summary>
         /// Visits list of <see cref="OpenApiTagReference"/> and child objects
         /// </summary>
-        internal void Walk(IList<OpenApiTagReference> tags)
+        internal void Walk(ISet<OpenApiTagReference> tags)
         {
             if (tags == null)
             {
@@ -94,9 +96,10 @@ internal void Walk(IList<OpenApiTagReference> tags)
             // Visit tags
             if (tags != null)
             {
-                for (var i = 0; i < tags.Count; i++)
+                var referencesAsArray = tags.ToArray();
+                for (var i = 0; i < referencesAsArray.Length; i++)
                 {
-                    Walk(i.ToString(), () => Walk(tags[i]));
+                    Walk(i.ToString(), () => Walk(referencesAsArray[i]));
                 }
             }
         }
@@ -1213,7 +1216,7 @@ internal void Walk(IOpenApiElement element)
                 case OpenApiServer e: Walk(e); break;
                 case OpenApiServerVariable e: Walk(e); break;
                 case OpenApiTag e: Walk(e); break;
-                case IList<OpenApiTag> e: Walk(e); break;
+                case ISet<OpenApiTag> e: Walk(e); break;
                 case IOpenApiExtensible e: Walk(e); break;
                 case IOpenApiExtension e: Walk(e); break;
             }
diff --git a/test/Microsoft.OpenApi.Hidi.Tests/UtilityFiles/OpenApiDocumentMock.cs b/test/Microsoft.OpenApi.Hidi.Tests/UtilityFiles/OpenApiDocumentMock.cs
index 3f81c71a3..0da220427 100644
--- a/test/Microsoft.OpenApi.Hidi.Tests/UtilityFiles/OpenApiDocumentMock.cs
+++ b/test/Microsoft.OpenApi.Hidi.Tests/UtilityFiles/OpenApiDocumentMock.cs
@@ -629,7 +629,7 @@ public static OpenApiDocument CreateOpenApiDocument()
                         }
                     }
                 },
-                Tags = new List<OpenApiTag>
+                Tags = new HashSet<OpenApiTag>
                 {
                     new()
                     {
@@ -678,18 +678,18 @@ public static OpenApiDocument CreateOpenApiDocument()
                     }
                 }
             };
-            document.Paths[getTeamsActivityByPeriodPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("reports.Functions", document));
-            document.Paths[getTeamsActivityByDatePath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("reports.Functions", document));
-            document.Paths[usersPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[usersByIdPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[usersByIdPath].Operations[OperationType.Patch].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[messagesByIdPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.message", document));
-            document.Paths[administrativeUnitRestorePath].Operations[OperationType.Post].Tags!.Add(new OpenApiTagReference("administrativeUnits.Actions", document));
-            document.Paths[logoPath].Operations[OperationType.Put].Tags!.Add(new OpenApiTagReference("applications.application", document));
-            document.Paths[securityProfilesPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("security.hostSecurityProfile", document));
-            document.Paths[communicationsCallsKeepAlivePath].Operations[OperationType.Post].Tags!.Add(new OpenApiTagReference("communications.Actions", document));
-            document.Paths[eventsDeltaPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("groups.Functions", document));
-            document.Paths[refPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("applications.directoryObject", document));
+            document.Paths[getTeamsActivityByPeriodPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("reports.Functions", document)};
+            document.Paths[getTeamsActivityByDatePath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("reports.Functions", document)};
+            document.Paths[usersPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[usersByIdPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[usersByIdPath].Operations[OperationType.Patch].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[messagesByIdPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.message", document)};
+            document.Paths[administrativeUnitRestorePath].Operations[OperationType.Post].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("administrativeUnits.Actions", document)};
+            document.Paths[logoPath].Operations[OperationType.Put].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("applications.application", document)};
+            document.Paths[securityProfilesPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("security.hostSecurityProfile", document)};
+            document.Paths[communicationsCallsKeepAlivePath].Operations[OperationType.Post].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("communications.Actions", document)};
+            document.Paths[eventsDeltaPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("groups.Functions", document)};
+            document.Paths[refPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("applications.directoryObject", document)};
             ((OpenApiSchema)document.Paths[usersPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema!.Properties["value"]).Items = new OpenApiSchemaReference("microsoft.graph.user", document);
             document.Paths[usersByIdPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema = new OpenApiSchemaReference("microsoft.graph.user", document);
             document.Paths[messagesByIdPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema = new OpenApiSchemaReference("microsoft.graph.message", document);
diff --git a/test/Microsoft.OpenApi.Readers.Tests/V2Tests/OpenApiOperationTests.cs b/test/Microsoft.OpenApi.Readers.Tests/V2Tests/OpenApiOperationTests.cs
index 13339332a..00c4faaeb 100644
--- a/test/Microsoft.OpenApi.Readers.Tests/V2Tests/OpenApiOperationTests.cs
+++ b/test/Microsoft.OpenApi.Readers.Tests/V2Tests/OpenApiOperationTests.cs
@@ -603,5 +603,48 @@ public async Task SerializesBodyReferencesWorks()
 """;
             Assert.True(JsonNode.DeepEquals(JsonNode.Parse(expected), JsonNode.Parse(actual)));
         }
+        [Fact]
+        public void DeduplicatesTagReferences()
+        {
+
+            var openApiDocument = new OpenApiDocument
+            {
+                Tags = new HashSet<OpenApiTag> { new() { Name = "user" } }
+            };
+            // Act
+            var expectedOp = new OpenApiOperation
+            {
+                Tags = new HashSet<OpenApiTagReference>
+                {
+                    new OpenApiTagReference("user", openApiDocument),
+                    new OpenApiTagReference("user", openApiDocument),
+                },
+                Summary = "Logs user into the system",
+                Description = "",
+                OperationId = "loginUser",
+                Parameters =
+                {
+                    new OpenApiParameter
+                    {
+                        Name = "password",
+                        Description = "The password for login in clear text",
+                        In = ParameterLocation.Query,
+                        Required = true,
+                        Schema = new OpenApiSchema()
+                        {
+                            Type = JsonSchemaType.String
+                        }
+                    }
+                }
+            };
+            using var textWriter = new StringWriter();
+            var writer = new OpenApiJsonWriter(textWriter);
+            expectedOp.SerializeAsV2(writer);
+            var result = textWriter.ToString();
+            var parsedJson = JsonNode.Parse(result);
+            var operationObject = Assert.IsType<JsonObject>(parsedJson);
+            var tags = Assert.IsType<JsonArray>(operationObject["tags"]);
+            Assert.Single(tags);
+        }
     }
 }
diff --git a/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs b/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs
index 83daf329d..5359162bf 100644
--- a/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs
+++ b/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs
@@ -724,7 +724,7 @@ public async Task ParseModifiedPetStoreDocumentWithTagAndSecurityShouldSucceed()
                         {
                             [OperationType.Get] = new OpenApiOperation
                             {
-                                Tags = new List<OpenApiTagReference>
+                                Tags = new HashSet<OpenApiTagReference>
                                     {
                                         tagReference1,
                                         tagReference2
@@ -812,7 +812,7 @@ public async Task ParseModifiedPetStoreDocumentWithTagAndSecurityShouldSucceed()
                             },
                             [OperationType.Post] = new OpenApiOperation
                             {
-                                Tags = new List<OpenApiTagReference>
+                                Tags = new HashSet<OpenApiTagReference>
                                     {
                                         tagReference1,
                                         tagReference2
@@ -1000,7 +1000,7 @@ public async Task ParseModifiedPetStoreDocumentWithTagAndSecurityShouldSucceed()
                     }
                 },
                 Components = components,
-                Tags = new List<OpenApiTag>
+                Tags = new HashSet<OpenApiTag>
                     {
                         new OpenApiTag
                         {
@@ -1032,15 +1032,8 @@ public async Task ParseModifiedPetStoreDocumentWithTagAndSecurityShouldSucceed()
 
             actual.Document.Should().BeEquivalentTo(expected, options => options
             .IgnoringCyclicReferences()
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags[0].Reference)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags[0].Reference.HostDocument)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags[0].Target)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Post].Tags[0].Reference.HostDocument)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Post].Tags[0].Target)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags[1].Reference.HostDocument)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags[1].Target)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Post].Tags[1].Reference.HostDocument)
-            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Post].Tags[1].Target)
+            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Get].Tags)
+            .Excluding(x => x.Paths["/pets"].Operations[OperationType.Post].Tags)
             .Excluding(x => x.Workspace)
             .Excluding(y => y.BaseUri));
 
diff --git a/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiOperationTests.cs b/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiOperationTests.cs
index 1dd24a128..c7a2317dc 100644
--- a/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiOperationTests.cs
+++ b/test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiOperationTests.cs
@@ -1,13 +1,16 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text.Json.Nodes;
 using System.Threading.Tasks;
 using FluentAssertions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
 using Microsoft.OpenApi.Reader;
+using Microsoft.OpenApi.Writers;
 using Xunit;
 
 namespace Microsoft.OpenApi.Readers.Tests.V3Tests
@@ -35,13 +38,13 @@ public async Task ParseOperationWithParameterWithNoLocationShouldSucceed()
         {
             var openApiDocument = new OpenApiDocument
             {
-                Tags = { new OpenApiTag() { Name = "user" } }
+                Tags = new HashSet<OpenApiTag> { new() { Name = "user" } }
             };
             // Act
             var operation = await OpenApiModelFactory.LoadAsync<OpenApiOperation>(Path.Combine(SampleFolderPath, "operationWithParameterWithNoLocation.json"), OpenApiSpecVersion.OpenApi3_0, openApiDocument);
             var expectedOp = new OpenApiOperation
             {
-                Tags =
+                Tags = new HashSet<OpenApiTagReference>()
                 {
                     new OpenApiTagReference("user", openApiDocument)
                 },
@@ -77,10 +80,50 @@ public async Task ParseOperationWithParameterWithNoLocationShouldSucceed()
             // Assert
             expectedOp.Should().BeEquivalentTo(operation, 
                 options => 
-                options.Excluding(x => x.Tags[0].Reference.HostDocument)
-                        .Excluding(x => x.Tags[0].Reference)
-                        .Excluding(x => x.Tags[0].Target)
-                        .Excluding(x => x.Tags[0].Extensions));
+                options.Excluding(x => x.Tags));
+        }
+        [Fact]
+        public void DeduplicatesTagReferences()
+        {
+
+            var openApiDocument = new OpenApiDocument
+            {
+                Tags = new HashSet<OpenApiTag> { new() { Name = "user" } }
+            };
+            // Act
+            var expectedOp = new OpenApiOperation
+            {
+                Tags = new HashSet<OpenApiTagReference>()
+                {
+                    new OpenApiTagReference("user", openApiDocument),
+                    new OpenApiTagReference("user", openApiDocument),
+                },
+                Summary = "Logs user into the system",
+                Description = "",
+                OperationId = "loginUser",
+                Parameters =
+                {
+                    new OpenApiParameter
+                    {
+                        Name = "password",
+                        Description = "The password for login in clear text",
+                        In = ParameterLocation.Query,
+                        Required = true,
+                        Schema = new OpenApiSchema()
+                        {
+                            Type = JsonSchemaType.String
+                        }
+                    }
+                }
+            };
+            using var textWriter = new StringWriter();
+            var writer = new OpenApiJsonWriter(textWriter);
+            expectedOp.SerializeAsV3(writer);
+            var result = textWriter.ToString();
+            var parsedJson = JsonNode.Parse(result);
+            var operationObject = Assert.IsType<JsonObject>(parsedJson);
+            var tags = Assert.IsType<JsonArray>(operationObject["tags"]);
+            Assert.Single(tags);
         }
     }
 }
diff --git a/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs b/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
index 3716a0b32..35e52cc59 100644
--- a/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
@@ -2078,7 +2078,7 @@ public async Task SerializeDocumentTagsWithMultipleExtensionsWorks()
                     Version = "1.0.0"
                 },
                 Paths = new OpenApiPaths(),
-                Tags = new List<OpenApiTag>
+                Tags = new HashSet<OpenApiTag>
                 {
                     new OpenApiTag
                     {
@@ -2102,5 +2102,42 @@ public async Task SerializeDocumentTagsWithMultipleExtensionsWorks()
             var actual = await doc.SerializeAsJsonAsync(OpenApiSpecVersion.OpenApi3_0);
             Assert.Equal(expected.MakeLineBreaksEnvironmentNeutral(), actual.MakeLineBreaksEnvironmentNeutral());
         }
+        [Fact]
+        public void DeduplicatesTags()
+        {
+            var document = new OpenApiDocument
+            {
+                Tags = new HashSet<OpenApiTag>
+                {
+                    new OpenApiTag
+                    {
+                        Name = "tag1",
+                        Extensions = new Dictionary<string, IOpenApiExtension>
+                        {
+                            ["x-tag1"] = new OpenApiAny("tag1")
+                        }
+                    },
+                    new OpenApiTag
+                    {
+                        Name = "tag2",
+                        Extensions = new Dictionary<string, IOpenApiExtension>
+                        {
+                            ["x-tag2"] = new OpenApiAny("tag2")
+                        }
+                    },
+                    new OpenApiTag
+                    {
+                        Name = "tag1",
+                        Extensions = new Dictionary<string, IOpenApiExtension>
+                        {
+                            ["x-tag1"] = new OpenApiAny("tag1")
+                        }
+                    }
+                }
+            };
+            Assert.Equal(2, document.Tags.Count);
+            Assert.Contains(document.Tags, t => t.Name == "tag1");
+            Assert.Contains(document.Tags, t => t.Name == "tag2");
+        }
     }
 }
diff --git a/test/Microsoft.OpenApi.Tests/Models/OpenApiOperationTests.cs b/test/Microsoft.OpenApi.Tests/Models/OpenApiOperationTests.cs
index af22284b9..31a26f1be 100644
--- a/test/Microsoft.OpenApi.Tests/Models/OpenApiOperationTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Models/OpenApiOperationTests.cs
@@ -89,9 +89,9 @@ public class OpenApiOperationTests
 
         private static OpenApiOperation _advancedOperationWithTagsAndSecurity => new()
         {
-            Tags = new List<OpenApiTagReference>
+            Tags = new HashSet<OpenApiTagReference>
             {
-                new OpenApiTagReference("tagId1", new OpenApiDocument{ Tags = new List<OpenApiTag>() { new OpenApiTag{Name = "tagId1"}} })
+                new OpenApiTagReference("tagId1", new OpenApiDocument{ Tags = new HashSet<OpenApiTag>() { new OpenApiTag{Name = "tagId1"}} })
             },
             Summary = "summary1",
             Description = "operationDescription",
diff --git a/test/Microsoft.OpenApi.Tests/OpenApiTagComparerTests.cs b/test/Microsoft.OpenApi.Tests/OpenApiTagComparerTests.cs
new file mode 100644
index 000000000..9ea0c498c
--- /dev/null
+++ b/test/Microsoft.OpenApi.Tests/OpenApiTagComparerTests.cs
@@ -0,0 +1,40 @@
+using Microsoft.OpenApi.Models;
+using Xunit;
+
+namespace Microsoft.OpenApi.Tests;
+
+public class OpenApiTagComparerTests
+{
+    private readonly OpenApiTagComparer _comparer = OpenApiTagComparer.Instance;
+    [Fact]
+    public void Defensive()
+    {
+        Assert.NotNull(_comparer);
+
+        Assert.True(_comparer.Equals(null, null));
+        Assert.False(_comparer.Equals(null, new OpenApiTag()));
+        Assert.Equal(0, _comparer.GetHashCode(null));
+        Assert.Equal(0, _comparer.GetHashCode(new OpenApiTag()));
+    }
+    [Fact]
+    public void SameNamesAreEqual()
+    {
+        var openApiTag1 = new OpenApiTag { Name = "tag" };
+        var openApiTag2 = new OpenApiTag { Name = "tag" };
+        Assert.True(_comparer.Equals(openApiTag1, openApiTag2));
+    }
+    [Fact]
+    public void SameInstanceAreEqual()
+    {
+        var openApiTag = new OpenApiTag { Name = "tag" };
+        Assert.True(_comparer.Equals(openApiTag, openApiTag));
+    }
+
+    [Fact]
+    public void DifferentCasingAreNotEquals()
+    {
+        var openApiTag1 = new OpenApiTag { Name = "tag" };
+        var openApiTag2 = new OpenApiTag { Name = "TAG" };
+        Assert.False(_comparer.Equals(openApiTag1, openApiTag2));
+    }
+}
diff --git a/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt b/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
index ca8c30327..6686f1446 100644
--- a/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
+++ b/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
@@ -722,7 +722,7 @@ namespace Microsoft.OpenApi.Models
         public Microsoft.OpenApi.Models.OpenApiPaths Paths { get; set; }
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiSecurityRequirement>? SecurityRequirements { get; set; }
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiServer>? Servers { get; set; }
-        public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiTag>? Tags { get; set; }
+        public System.Collections.Generic.ISet<Microsoft.OpenApi.Models.OpenApiTag>? Tags { get; set; }
         public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.Models.Interfaces.IOpenApiPathItem>? Webhooks { get; set; }
         public Microsoft.OpenApi.Services.OpenApiWorkspace? Workspace { get; set; }
         public bool AddComponent<T>(string id, T componentToRegister) { }
@@ -914,7 +914,7 @@ namespace Microsoft.OpenApi.Models
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiSecurityRequirement>? Security { get; set; }
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiServer>? Servers { get; set; }
         public string? Summary { get; set; }
-        public System.Collections.Generic.IList<Microsoft.OpenApi.Models.References.OpenApiTagReference>? Tags { get; set; }
+        public System.Collections.Generic.ISet<Microsoft.OpenApi.Models.References.OpenApiTagReference>? Tags { get; set; }
         public void SerializeAsV2(Microsoft.OpenApi.Writers.IOpenApiWriter writer) { }
         public void SerializeAsV3(Microsoft.OpenApi.Writers.IOpenApiWriter writer) { }
         public void SerializeAsV31(Microsoft.OpenApi.Writers.IOpenApiWriter writer) { }
@@ -1664,8 +1664,8 @@ namespace Microsoft.OpenApi.Services
         public virtual void Visit(System.Collections.Generic.IList<Microsoft.OpenApi.Models.Interfaces.IOpenApiParameter> parameters) { }
         public virtual void Visit(System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiSecurityRequirement> openApiSecurityRequirements) { }
         public virtual void Visit(System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiServer> servers) { }
-        public virtual void Visit(System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiTag> openApiTags) { }
-        public virtual void Visit(System.Collections.Generic.IList<Microsoft.OpenApi.Models.References.OpenApiTagReference> openApiTags) { }
+        public virtual void Visit(System.Collections.Generic.ISet<Microsoft.OpenApi.Models.OpenApiTag> openApiTags) { }
+        public virtual void Visit(System.Collections.Generic.ISet<Microsoft.OpenApi.Models.References.OpenApiTagReference> openApiTags) { }
         public virtual void Visit(System.Text.Json.Nodes.JsonNode node) { }
     }
     public class OpenApiWalker
diff --git a/test/Microsoft.OpenApi.Tests/Visitors/InheritanceTests.cs b/test/Microsoft.OpenApi.Tests/Visitors/InheritanceTests.cs
index 581f2998a..44febe633 100644
--- a/test/Microsoft.OpenApi.Tests/Visitors/InheritanceTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Visitors/InheritanceTests.cs
@@ -53,7 +53,7 @@ public void ExpectedVirtualsInvolved()
             visitor.Visit(default(OpenApiSecurityRequirement));
             visitor.Visit(default(IOpenApiSecurityScheme));
             visitor.Visit(default(IOpenApiExample));
-            visitor.Visit(default(IList<OpenApiTag>));
+            visitor.Visit(default(ISet<OpenApiTag>));
             visitor.Visit(default(IList<OpenApiSecurityRequirement>));
             visitor.Visit(default(IOpenApiExtensible));
             visitor.Visit(default(IOpenApiExtension));
@@ -292,7 +292,7 @@ public override void Visit(IOpenApiExample example)
                 base.Visit(example);
             }
 
-            public override void Visit(IList<OpenApiTag> openApiTags)
+            public override void Visit(ISet<OpenApiTag> openApiTags)
             {
                 EncodeCall();
                 base.Visit(openApiTags);
diff --git a/test/Microsoft.OpenApi.Tests/Walkers/WalkerLocationTests.cs b/test/Microsoft.OpenApi.Tests/Walkers/WalkerLocationTests.cs
index ce45186c6..a2f66e0c8 100644
--- a/test/Microsoft.OpenApi.Tests/Walkers/WalkerLocationTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Walkers/WalkerLocationTests.cs
@@ -28,7 +28,6 @@ public void LocateTopLevelObjects()
                 "#/info",
                 "#/servers",
                 "#/paths",
-                "#/tags"
             }, locator.Locations);
         }
 
@@ -42,7 +41,7 @@ public void LocateTopLevelArrayItems()
                     new(),
                     new()
                 },
-                Tags = new List<OpenApiTag>
+                Tags = new HashSet<OpenApiTag>
                 {
                     new()
                 }
@@ -108,8 +107,6 @@ public void LocatePathOperationContentSchema()
                 "#/paths/~1test/get/responses/200/content",
                 "#/paths/~1test/get/responses/200/content/application~1json",
                 "#/paths/~1test/get/responses/200/content/application~1json/schema",
-                "#/paths/~1test/get/tags",
-                "#/tags",
 
             }, locator.Locations);
 
@@ -152,7 +149,6 @@ public void WalkDOMWithCycles()
                 "#/components",
                 "#/components/schemas/loopy",
                 "#/components/schemas/loopy/properties/name",
-                "#/tags"
             }, locator.Locations);
         }
 
@@ -305,7 +301,7 @@ public override void Visit(IOpenApiSchema schema)
             Locations.Add(this.PathString);
         }
 
-        public override void Visit(IList<OpenApiTag> openApiTags)
+        public override void Visit(ISet<OpenApiTag> openApiTags)
         {
             Locations.Add(this.PathString);
         }
@@ -319,7 +315,7 @@ public override void Visit(OpenApiServer server)
         {
             Locations.Add(this.PathString);
         }
-        public override void Visit(IList<OpenApiTagReference> openApiTags)
+        public override void Visit(ISet<OpenApiTagReference> openApiTags)
         {
             Locations.Add(this.PathString);
         }