diff --git a/String/CountWords.js b/String/CountWords.js
new file mode 100644
index 0000000000..5c04a36e59
--- /dev/null
+++ b/String/CountWords.js
@@ -0,0 +1,19 @@
+/**
+ * @function countWords
+ * @description Counts the number of words in a given string.
+ *   Words are separated by whitespace.
+ * @param {string} str - The input string
+ * @returns {number} - The number of words in the string
+ * @see https://en.wikipedia.org/wiki/Word_count
+ * @example countWords("Hello World") => 2
+ * @example countWords("  Hello   World  ") => 2
+ * @example countWords("") => 0
+ */
+const countWords = (str) => {
+  if (typeof str !== 'string') {
+    throw new TypeError('Input must be a string')
+  }
+  return str.trim() === '' ? 0 : str.trim().split(/\s+/).length
+}
+
+export { countWords }
diff --git a/String/test/CountWords.test.js b/String/test/CountWords.test.js
new file mode 100644
index 0000000000..9defd7976d
--- /dev/null
+++ b/String/test/CountWords.test.js
@@ -0,0 +1,39 @@
+import { countWords } from '../CountWords.js'
+
+describe('countWords', () => {
+  test("countWords('Hello World') returns 2", () => {
+    expect(countWords('Hello World')).toBe(2)
+  })
+
+  test("countWords('') returns 0", () => {
+    expect(countWords('')).toBe(0)
+  })
+
+  test("countWords('  Hello   World  ') returns 2", () => {
+    expect(countWords('  Hello   World  ')).toBe(2)
+  })
+
+  test('countWords single word returns 1', () => {
+    expect(countWords('JavaScript')).toBe(1)
+  })
+
+  test("countWords('The quick brown fox') returns 4", () => {
+    expect(countWords('The quick brown fox')).toBe(4)
+  })
+
+  test('countWords with tabs and newlines', () => {
+    expect(countWords('hello\tworld\nfoo')).toBe(3)
+  })
+
+  test('countWords with only spaces returns 0', () => {
+    expect(countWords('     ')).toBe(0)
+  })
+
+  test('throws TypeError for non-string input', () => {
+    expect(() => countWords(123)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for null input', () => {
+    expect(() => countWords(null)).toThrow(TypeError)
+  })
+})