diff --git a/tests/test_decoder.py b/tests/test_decoder.py
index f808fc5..7ab7576 100644
--- a/tests/test_decoder.py
+++ b/tests/test_decoder.py
@@ -56,6 +56,15 @@
     )
 assert _STEP_SPECIFICATION_VARIABLE_NAMES_WORKFLOW
 
+_WORKFLOW_OPTIONS_WORKFLOW_FILE: str = os.path.join(
+    os.path.dirname(__file__),
+    "workflow-definitions",
+    "workflow-options.yaml",
+)
+with open(_WORKFLOW_OPTIONS_WORKFLOW_FILE, "r", encoding="utf8") as workflow_file:
+    _WORKFLOW_OPTIONS: Dict[str, Any] = yaml.safe_load(workflow_file)
+assert _WORKFLOW_OPTIONS
+
 
 def test_validate_schema_for_minimal():
     # Arrange
@@ -133,6 +142,16 @@ def test_validate_schema_for_step_specification_variable_names():
     assert error is None
 
 
+def test_validate_schema_for_workflow_options():
+    # Arrange
+
+    # Act
+    error = decoder.validate_schema(_WORKFLOW_OPTIONS)
+
+    # Assert
+    assert error is None
+
+
 def test_get_workflow_variables_for_smiple_python_molprops():
     # Arrange
 
diff --git a/tests/test_workflow_validator_for_run_level.py b/tests/test_workflow_validator_for_run_level.py
index 725994d..e5fdfb6 100644
--- a/tests/test_workflow_validator_for_run_level.py
+++ b/tests/test_workflow_validator_for_run_level.py
@@ -131,6 +131,88 @@ def test_validate_simple_python_molprops():
     assert error.error_msg is None
 
 
+def test_validate_simple_python_molprops_with_options_when_missing_required():
+    # Arrange
+    workflow_file: str = os.path.join(
+        os.path.dirname(__file__),
+        "workflow-definitions",
+        "simple-python-molprops-with-options.yaml",
+    )
+    with open(workflow_file, "r", encoding="utf8") as workflow_file:
+        workflow: dict[str, Any] = yaml.load(workflow_file, Loader=yaml.FullLoader)
+    assert workflow
+    variables = {
+        "candidateMolecules": "input.sdf",
+        "clusteredMolecules": "output.sdf",
+    }
+
+    # Act
+    error = WorkflowValidator.validate(
+        level=ValidationLevel.RUN,
+        workflow_definition=workflow,
+        variables=variables,
+    )
+
+    # Assert
+    assert error.error_num == 7
+    assert error.error_msg == [
+        "Missing workflow variable values for: rdkitPropertyValue"
+    ]
+
+
+def test_validate_simple_python_molprops_with_options():
+    # Arrange
+    workflow_file: str = os.path.join(
+        os.path.dirname(__file__),
+        "workflow-definitions",
+        "simple-python-molprops-with-options.yaml",
+    )
+    with open(workflow_file, "r", encoding="utf8") as workflow_file:
+        workflow: dict[str, Any] = yaml.load(workflow_file, Loader=yaml.FullLoader)
+    assert workflow
+    variables = {
+        "candidateMolecules": "input.sdf",
+        "clusteredMolecules": "output.sdf",
+        "rdkitPropertyName": "col1",
+        "rdkitPropertyValue": 123,
+    }
+
+    # Act
+    error = WorkflowValidator.validate(
+        level=ValidationLevel.RUN,
+        workflow_definition=workflow,
+        variables=variables,
+    )
+
+    # Assert
+    assert error.error_num == 0
+    assert error.error_msg is None
+
+
+def test_validate_simple_python_molprops_with_missing_input():
+    # Arrange
+    workflow_file: str = os.path.join(
+        os.path.dirname(__file__), "workflow-definitions", "simple-python-molprops.yaml"
+    )
+    with open(workflow_file, "r", encoding="utf8") as workflow_file:
+        workflow: dict[str, Any] = yaml.load(workflow_file, Loader=yaml.FullLoader)
+    assert workflow
+    variables = {"clusteredMolecules": "output.sdf"}
+
+    # Act
+    error = WorkflowValidator.validate(
+        level=ValidationLevel.RUN,
+        workflow_definition=workflow,
+        variables=variables,
+    )
+
+    # Assert
+    assert error.error_num == 7
+    assert error.error_msg == [
+        "Missing workflow variable values for: candidateMolecules"
+    ]
+
+
 def test_validate_duplicate_workflow_variable_names():
     # Arrange
     workflow_file: str = os.path.join(
diff --git a/tests/workflow-definitions/duplicate-step-names.yaml b/tests/workflow-definitions/duplicate-step-names.yaml
index f89d610..78fe11a 100644
--- a/tests/workflow-definitions/duplicate-step-names.yaml
+++ b/tests/workflow-definitions/duplicate-step-names.yaml
@@ -2,12 +2,15 @@
 kind: DataManagerWorkflow
 kind-version: "2024.1"
 name: duplicate-step-names
+
 steps:
+
 - name: step-1
   specification:
     collection: a
     job: b
     version: '1.0.0'
+
 - name: step-1
   specification:
     collection: a
diff --git a/tests/workflow-definitions/duplicate-workflow-variable-names.yaml b/tests/workflow-definitions/duplicate-workflow-variable-names.yaml
index 7649404..3f8c6f1 100644
--- a/tests/workflow-definitions/duplicate-workflow-variable-names.yaml
+++ b/tests/workflow-definitions/duplicate-workflow-variable-names.yaml
@@ -15,6 +15,7 @@ variables:
     as: clustered-molecules.smi
 
 steps:
+
 - name: step1
   description: Add column 1
   specification:
diff --git a/tests/workflow-definitions/example-nop-fail.yaml b/tests/workflow-definitions/example-nop-fail.yaml
index f265988..ed1a172 100644
--- a/tests/workflow-definitions/example-nop-fail.yaml
+++ b/tests/workflow-definitions/example-nop-fail.yaml
@@ -4,7 +4,9 @@ kind-version: "2024.1"
 name: nop-fail
 description: >-
   A workflow with one step that fails
+
 steps:
+
 - name: step-1
   specification:
     collection: workflow-engine-unit-test-jobs
diff --git a/tests/workflow-definitions/example-smiles-to-file.yaml b/tests/workflow-definitions/example-smiles-to-file.yaml
index e543050..246e410 100644
--- a/tests/workflow-definitions/example-smiles-to-file.yaml
+++ b/tests/workflow-definitions/example-smiles-to-file.yaml
@@ -5,7 +5,9 @@ name: smiles-to-file
 description: >-
   A workflow with one step that uses variables.
   The step takes an input string and the Job creates a file from it.
+
 steps:
+
 - name: step-1
   specification:
     collection: workflow-engine-unit-test-jobs
diff --git a/tests/workflow-definitions/example-two-step-nop.yaml b/tests/workflow-definitions/example-two-step-nop.yaml
index df64b9a..6fc2a7a 100644
--- a/tests/workflow-definitions/example-two-step-nop.yaml
+++ b/tests/workflow-definitions/example-two-step-nop.yaml
@@ -5,12 +5,15 @@ name: two-step-nop
 description: >-
   A workflow with two steps.
   The steps do nothing, take no arguments, and simply return success.
+
 steps:
+
 - name: step-1
   specification:
     collection: workflow-engine-unit-test-jobs
     job: nop
     version: "1.0.0"
+
 - name: step-2
   specification:
     collection: workflow-engine-unit-test-jobs
diff --git a/tests/workflow-definitions/minimal.yaml b/tests/workflow-definitions/minimal.yaml
index d2dd2cb..4e6045d 100644
--- a/tests/workflow-definitions/minimal.yaml
+++ b/tests/workflow-definitions/minimal.yaml
@@ -2,7 +2,9 @@
 kind: DataManagerWorkflow
 kind-version: "2024.1"
 name: workflow-minimal
+
 steps:
+
 - name: step-1
   specification:
     collection: a
diff --git a/tests/workflow-definitions/shortcut-example-1.yaml b/tests/workflow-definitions/shortcut-example-1.yaml
index a9446e7..494af9b 100644
--- a/tests/workflow-definitions/shortcut-example-1.yaml
+++ b/tests/workflow-definitions/shortcut-example-1.yaml
@@ -3,7 +3,9 @@ kind: DataManagerWorkflow
 kind-version: "2024.1"
 name: shortcut-example-1
 description: The shortcut example 1 workflow
+
 steps:
+
 - name: example-1-step-1
   description: The first step
   specification:
@@ -13,6 +15,7 @@ steps:
   outputs:
   - output: 'outputFile'
     as: 'a.sdf'
+
 - name: example-1-step-2
   description: The first step
   specification:
diff --git a/tests/workflow-definitions/simple-python-molprops-with-options.yaml b/tests/workflow-definitions/simple-python-molprops-with-options.yaml
new file mode 100644
index 0000000..61f7ad8
--- /dev/null
+++ b/tests/workflow-definitions/simple-python-molprops-with-options.yaml
@@ -0,0 +1,59 @@
+---
+kind: DataManagerWorkflow
+kind-version: "2024.1"
+name: python-workflow
+description: A simple python experimental workflow
+variables:
+  inputs:
+  - name: candidateMolecules
+    type: squonk/x-smiles
+  outputs:
+  - name: clusteredMolecules
+    from:
+      step: step2
+      output: outputFile
+    as: clustered-molecules.smi
+  options:
+  - name: rdkitPropertyName
+    default: name
+    as:
+    - option: name
+      step: step1
+  - name: rdkitPropertyValue
+    as:
+    - option: value
+      step: step1
+
+steps:
+
+- name: step1
+  description: Add column 1
+  specification:
+    collection: workflow-engine-unit-test-jobs
+    job: rdkit-molprops
+    version: "1.0.0"
+  inputs:
+  - input: inputFile
+    from:
+      workflow-input: candidateMolecules
+  outputs:
+  - output: outputFile
+    as: step1.out.smi
+
+- name: step2
+  description: Add column 2
+  specification:
+    collection: workflow-engine-unit-test-jobs
+    job: cluster-butina
+    version: "1.0.0"
+    variables:
+      name: "col2"
+      value: "999"
+  inputs:
+  - input: inputFile
+    from:
+      step: step1
+      output: outputFile
+  outputs:
+  - output: outputFile
+    as: step2.out.smi
diff --git a/tests/workflow-definitions/simple-python-molprops.yaml b/tests/workflow-definitions/simple-python-molprops.yaml
index aeeeafe..aa761a7 100644
--- a/tests/workflow-definitions/simple-python-molprops.yaml
+++ b/tests/workflow-definitions/simple-python-molprops.yaml
@@ -15,6 +15,7 @@ variables:
     as: clustered-molecules.smi
 
 steps:
+
 - name: step1
   description: Add column 1
   specification:
diff --git a/tests/workflow-definitions/step-specification-variable-names.yaml b/tests/workflow-definitions/step-specification-variable-names.yaml
index 0a9bbca..a7db65b 100644
--- a/tests/workflow-definitions/step-specification-variable-names.yaml
+++ b/tests/workflow-definitions/step-specification-variable-names.yaml
@@ -3,14 +3,16 @@ kind: DataManagerWorkflow
 kind-version: "2024.1"
 name: step-variables
 description: Test a lot of variables whose format is supported
+
 steps:
+
 - name: step-1
   specification:
     collection: a
     job: b
     version: '1.0.0'
     variables:
-      _a: 1
-      A-1: 2.0
+      a: 1
+      A_1: 2.0
       a_14_: A string
-      A-Long_boolean_variable_Name: true
+      A_Long_boolean_variableName: true
diff --git a/tests/workflow-definitions/workflow-options.yaml b/tests/workflow-definitions/workflow-options.yaml
new file mode 100644
index 0000000..a0392c0
--- /dev/null
+++ b/tests/workflow-definitions/workflow-options.yaml
@@ -0,0 +1,54 @@
+---
+kind: DataManagerWorkflow
+kind-version: "2024.1"
+name: workflow-options
+description: Illustrate the use of workflow options
+variables:
+  options:
+  - name: variableWithoutDefault
+    as:
+    - option: variable1
+      step: step-1
+    - option: variable2
+      step: step-2
+  - name: variableWithIntegerDefault
+    default: 7
+    as:
+    - option: variable3
+      step: step-1
+  - name: variableWithIntegerDefaultAndRange
+    default: 7
+    minimum: 1
+    maximum: 8
+    as:
+    - option: variable4
+      step: step-1
+  - name: variableWithFloatDefault
+    default: 1.0
+    as:
+    - option: variable5
+      step: step-1
+  - name: variableWithBooleanDefault
+    default: true
+    as:
+    - option: variable6
+      step: step-1
+  - name: variableWithStringDefault
+    default: Hello, World!
+    as:
+    - option: variable7
+      step: step-1
+
+steps:
+
+- name: step-1
+  specification:
+    collection: a
+    job: b
+    version: '1.0.0'
+
+- name: step-2
+  specification:
+    collection: a
+    job: b
+    version: '1.0.0'
diff --git a/workflow/decoder.py b/workflow/decoder.py
index 5a0fb8c..7b976ed 100644
--- a/workflow/decoder.py
+++ b/workflow/decoder.py
@@ -64,7 +64,8 @@ def get_description(definition: dict[str, Any]) -> str | None:
 
 def get_variable_names(definition: dict[str, Any]) -> list[str]:
     """Given a Workflow definition this function returns all the names of the
-    variables defined at the workflow level. This function DOES NOT deduplicate names,
+    variables defined at the workflow level. These are the 'names' for inputs,
+    outputs and options. This function DOES NOT de-duplicate names,
     that is the role of the validator."""
     wf_variable_names: list[str] = []
     variables: dict[str, Any] | None = definition.get("variables")
@@ -75,6 +76,9 @@ def get_variable_names(definition: dict[str, Any]) -> list[str]:
         wf_variable_names.extend(
             output_variable["name"] for output_variable in variables.get("outputs", [])
         )
+        wf_variable_names.extend(
+            option_variable["name"] for option_variable in variables.get("options", [])
+        )
     return wf_variable_names
 
 
@@ -85,8 +89,16 @@ def get_required_variable_names(definition: dict[str, Any]) -> list[str]:
     required_variables: list[str] = []
     variables: dict[str, Any] | None = definition.get("variables")
     if variables:
-        # For now, all inputs are required...
+        # All inputs are required (no defaults atm)...
         required_variables.extend(
             input_variable["name"] for input_variable in variables.get("inputs", [])
         )
+        # Options without defaults are required...
+        # It is the role of the engine to provide the actual default for those
+        # that have defaults but no user-defined value.
+        required_variables.extend(
+            option_variable["name"]
+            for option_variable in variables.get("options", [])
+            if "default" not in option_variable
+        )
     return required_variables
diff --git a/workflow/workflow-schema.yaml b/workflow/workflow-schema.yaml
index 07f018f..0481405 100644
--- a/workflow/workflow-schema.yaml
+++ b/workflow/workflow-schema.yaml
@@ -29,6 +29,7 @@ properties:
       $ref: "#/definitions/step"
   variables:
     type: object
+    additionalProperties: false
     properties:
       inputs:
         type: array
@@ -38,6 +39,10 @@ properties:
         type: array
         items:
           $ref: "#/definitions/workflow-output-parameter"
+      options:
+        type: array
+        items:
+          $ref: "#/definitions/workflow-option-parameter"
 required:
 - kind
 - kind-version
@@ -100,6 +105,20 @@ definitions:
     - name
     - as
 
+  # Declaration of a value from a workflow input (variable)
+  as-step-option:
+    type: object
+    additionalProperties: false
+    properties:
+      option:
+        $ref: '#/definitions/template-variable-name'
+      step:
+        $ref: '#/definitions/rfc1035-label-name'
+    required:
+    - option
+    - step
+
+
   # Declaration of a value from a workflow input (variable)
   from-workflow-input:
     type: object
@@ -123,6 +142,34 @@ definitions:
     - step
     - output
 
+  # A workflow option used as a step option
+  workflow-option-parameter:
+    type: object
+    additionalProperties: false
+    properties:
+      name:
+        $ref: '#/definitions/template-variable-name'
+      description:
+        type: string
+      default:
+        oneOf:
+        - type: string
+        - type: number
+        - type: boolean
+      minimum:
+        oneOf:
+        - type: number
+      maximum:
+        oneOf:
+        - type: number
+      as:
+        type: array
+        items:
+          $ref: '#/definitions/as-step-option'
+    required:
+    - name
+    - as
+
   # A Step input (from an output of a prior step)
   step-input-from-step:
     type: object
@@ -172,7 +219,7 @@ definitions:
     type: object
     additionalProperties: false
     patternProperties:
-      '^[a-zA-Z_]{1}[a-zA-Z0-9_-]{0,79}$':
+      '^[a-zA-Z]{1}[a-zA-Z0-9_]{0,79}$':
         oneOf:
         - type: string
         - type: integer