diff --git a/src/main/java/com/thealgorithms/strings/Isogram.java b/src/main/java/com/thealgorithms/strings/Isogram.java
new file mode 100644
index 000000000000..b37f085b075d
--- /dev/null
+++ b/src/main/java/com/thealgorithms/strings/Isogram.java
@@ -0,0 +1,92 @@
+package com.thealgorithms.strings;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * An isogram (also called heterogram or nonpattern word) is a word in which no
+ * letter of the word occurs more than once. Each character appears exactly
+ * once.
+ *
+ * For example, the word "uncopyrightable" is the longest common English isogram
+ * with 15 unique letters. Other examples include "dermatoglyphics" (15
+ * letters),
+ * "background" (10 letters), "python" (6 letters), and "keyboard" (8 letters).
+ * But words like "hello" and "programming" are not isograms because some
+ * letters
+ * appear multiple times ('l' appears twice in "hello", while 'r', 'm', 'g'
+ * repeat
+ * in "programming").
+ *
+ * Isograms are particularly valuable in creating substitution ciphers and are
+ * studied in recreational linguistics. A perfect pangram, which uses all 26
+ * letters
+ * of the alphabet exactly once, is a special type of isogram.
+ *
+ * Reference from https://en.wikipedia.org/wiki/Heterogram_(literature)#Isograms
+ */
+public final class Isogram {
+    /**
+     * Private constructor to prevent instantiation of utility class.
+     */
+    private Isogram() {
+    }
+
+    /**
+     * Checks if a string is an isogram using boolean array approach.
+     *
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     *
+     * @param str the input string
+     * @return true if the string is an isogram, false otherwise
+     * @throws IllegalArgumentException if the string contains non-alphabetic
+     *                                  characters
+     */
+    public static boolean isAlphabeticIsogram(String str) {
+        if (str == null || str.isEmpty()) {
+            return true;
+        }
+
+        str = str.toLowerCase();
+
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            if (ch < 'a' || ch > 'z') {
+                throw new IllegalArgumentException("Input contains non-alphabetic character: '" + ch + "'");
+            }
+        }
+
+        boolean[] seenChars = new boolean[26];
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            int index = ch - 'a';
+            if (seenChars[index]) {
+                return false;
+            }
+            seenChars[index] = true;
+        }
+        return true;
+    }
+
+    /**
+     * Checks if a string is an isogram using length comparison approach.
+     * Time Complexity: O(n)
+     * Space Complexity: O(k) where k is the number of unique characters
+     *
+     * @param str the input string
+     * @return true if the string is an isogram, false otherwise
+     */
+    public static boolean isFullIsogram(String str) {
+        if (str == null || str.isEmpty()) {
+            return true;
+        }
+        str = str.toLowerCase();
+
+        Set<Character> uniqueChars = new HashSet<>();
+        for (char ch : str.toCharArray()) {
+            uniqueChars.add(ch);
+        }
+        return uniqueChars.size() == str.length();
+    }
+}
diff --git a/src/test/java/com/thealgorithms/strings/IsogramTest.java b/src/test/java/com/thealgorithms/strings/IsogramTest.java
new file mode 100644
index 000000000000..9dd844dc7cf9
--- /dev/null
+++ b/src/test/java/com/thealgorithms/strings/IsogramTest.java
@@ -0,0 +1,117 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class IsogramTest {
+
+    record IsogramTestCase(String input, boolean expected) {
+    }
+
+    private static Stream<IsogramTestCase> isAlphabeticIsogram() {
+        return Stream.of(
+            // Valid isograms (only checks letters)
+            new IsogramTestCase("uncopyrightable", true), new IsogramTestCase("dermatoglyphics", true), new IsogramTestCase("background", true), new IsogramTestCase("python", true), new IsogramTestCase("keyboard", true), new IsogramTestCase("clipboard", true), new IsogramTestCase("flowchart", true),
+            new IsogramTestCase("bankruptcy", true), new IsogramTestCase("computer", true), new IsogramTestCase("algorithms", true),
+
+            // Not isograms - letters repeat
+            new IsogramTestCase("hello", false), new IsogramTestCase("programming", false), new IsogramTestCase("java", false), new IsogramTestCase("coffee", false), new IsogramTestCase("book", false), new IsogramTestCase("letter", false), new IsogramTestCase("mississippi", false),
+            new IsogramTestCase("google", false),
+
+            // Edge cases
+            new IsogramTestCase("", true), new IsogramTestCase("a", true), new IsogramTestCase("ab", true), new IsogramTestCase("abc", true), new IsogramTestCase("aa", false), new IsogramTestCase("abcdefghijklmnopqrstuvwxyz", true),
+
+            // Case insensitive
+            new IsogramTestCase("Python", true), new IsogramTestCase("BACKGROUND", true), new IsogramTestCase("Hello", false), new IsogramTestCase("PROGRAMMING", false));
+    }
+
+    private static Stream<IsogramTestCase> isFullIsogram() {
+        return Stream.of(
+            // Valid isograms (checks all characters)
+            new IsogramTestCase("uncopyrightable", true), new IsogramTestCase("dermatoglyphics", true), new IsogramTestCase("background", true), new IsogramTestCase("python", true), new IsogramTestCase("keyboard", true), new IsogramTestCase("clipboard", true), new IsogramTestCase("flowchart", true),
+            new IsogramTestCase("bankruptcy", true), new IsogramTestCase("computer", true), new IsogramTestCase("algorithms", true),
+
+            // Not isograms - characters repeat
+            new IsogramTestCase("hello", false), new IsogramTestCase("programming", false), new IsogramTestCase("java", false), new IsogramTestCase("coffee", false), new IsogramTestCase("book", false), new IsogramTestCase("letter", false), new IsogramTestCase("mississippi", false),
+            new IsogramTestCase("google", false),
+
+            // Edge cases
+            new IsogramTestCase("", true), new IsogramTestCase("a", true), new IsogramTestCase("ab", true), new IsogramTestCase("abc", true), new IsogramTestCase("aa", false), new IsogramTestCase("abcdefghijklmnopqrstuvwxyz", true),
+
+            // Case insensitive
+            new IsogramTestCase("Python", true), new IsogramTestCase("BACKGROUND", true), new IsogramTestCase("Hello", false), new IsogramTestCase("PROGRAMMING", false),
+
+            // Strings with symbols and numbers
+            new IsogramTestCase("abc@def", true), // all characters unique
+            new IsogramTestCase("test-case", false), // 't', 's', 'e' repeat
+            new IsogramTestCase("python123", true), // all characters unique
+            new IsogramTestCase("hello@123", false), // 'l' repeats
+            new IsogramTestCase("abc123!@#", true), // all characters unique
+            new IsogramTestCase("test123test", false), // 't', 'e', 's' repeat
+            new IsogramTestCase("1234567890", true), // all digits unique
+            new IsogramTestCase("12321", false), // '1' and '2' repeat
+            new IsogramTestCase("!@#$%^&*()", true) // all special characters unique
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("isAlphabeticIsogram")
+    void testIsogramByArray(IsogramTestCase testCase) {
+        assertEquals(testCase.expected(), Isogram.isAlphabeticIsogram(testCase.input()));
+    }
+
+    @ParameterizedTest
+    @MethodSource("isFullIsogram")
+    void testIsogramByLength(IsogramTestCase testCase) {
+        assertEquals(testCase.expected(), Isogram.isFullIsogram(testCase.input()));
+    }
+
+    @Test
+    void testNullInputByArray() {
+        assertTrue(Isogram.isAlphabeticIsogram(null));
+    }
+
+    @Test
+    void testNullInputByLength() {
+        assertTrue(Isogram.isFullIsogram(null));
+    }
+
+    @Test
+    void testEmptyStringByArray() {
+        assertTrue(Isogram.isAlphabeticIsogram(""));
+    }
+
+    @Test
+    void testEmptyStringByLength() {
+        assertTrue(Isogram.isFullIsogram(""));
+    }
+
+    @Test
+    void testAlphabeticIsogramThrowsException() {
+        // Test that IllegalArgumentException is thrown for non-alphabetic characters
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("1"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("@"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("python!"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("123algorithm"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("hello123"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("!@@#$%^&*()"));
+    }
+
+    @Test
+    void testFullIsogramWithMixedCharacters() {
+        // Test that full isogram method handles all character types without exceptions
+        assertTrue(Isogram.isFullIsogram("abc123"));
+        assertFalse(Isogram.isFullIsogram("test@email")); // 'e' repeats
+        assertFalse(Isogram.isFullIsogram("hello123")); // 'l' repeats
+        assertTrue(Isogram.isFullIsogram("1234567890"));
+        assertFalse(Isogram.isFullIsogram("12321")); // '1' and '2' repeat
+        assertTrue(Isogram.isFullIsogram("!@#$%^&*()"));
+    }
+}