diff --git a/README.md b/README.md
index da6eff8..4bc522b 100644
--- a/README.md
+++ b/README.md
@@ -98,6 +98,7 @@ It also only work with common ASCII characters characters. We don't plan to supp
   - [charAt](#charat)
   - [concat](#concat)
   - [endsWith](#endsWith)
+  - [includes](#includes)
   - [join](#join)
   - [length](#length)
   - [padEnd](#padend)
@@ -208,6 +209,17 @@ const result = endsWith('abc', 'c')
 //    ^ true
 ```
 
+### includes
+
+This function is a strongly-typed counterpart of `String.prototype.includes`.
+
+```ts
+import { includes } from 'string-ts'
+
+const result = includes('abcde', 'bcd')
+//    ^ true
+```
+
 ### join
 
 This function is a strongly-typed counterpart of `Array.prototype.join`.
@@ -712,6 +724,7 @@ Uppercase<'hello world'> // 'HELLO WORLD'
 St.CharAt<'hello world', 6> // 'w'
 St.Concat<['a', 'bc', 'def']> // 'abcdef'
 St.EndsWith<'abc', 'c'> // true
+St.Includes<'abcde', 'bcd'> // true
 St.Join<['hello', 'world'], '-'> // 'hello-world'
 St.Length<'hello'> // 5
 St.PadEnd<'hello', 10, '='> // 'hello====='
diff --git a/src/index.ts b/src/index.ts
index cc56e8e..91f41bf 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,6 +3,7 @@ export type {
   CharAt,
   Concat,
   EndsWith,
+  Includes,
   Join,
   Length,
   PadEnd,
@@ -21,6 +22,7 @@ export {
   charAt,
   concat,
   endsWith,
+  includes,
   join,
   length,
   padEnd,
diff --git a/src/primitives.test.ts b/src/primitives.test.ts
index 32c367b..a0a82d8 100644
--- a/src/primitives.test.ts
+++ b/src/primitives.test.ts
@@ -39,6 +39,7 @@ namespace TypeTests {
 
   type test12 = Expect<Equal<Subject.StartsWith<'abc', 'a'>, true>>
   type test13 = Expect<Equal<Subject.EndsWith<'abc', 'c'>, true>>
+  type test14 = Expect<Equal<Subject.Includes<'abcde', 'bcd'>, true>>
 }
 
 beforeEach(() => {
@@ -55,6 +56,102 @@ describe('primitives', () => {
     })
   })
 
+  describe('endsWith', () => {
+    const text = 'abc'
+
+    describe('without offset', () => {
+      test('should return true when text ends with search', () => {
+        const result = subject.endsWith(text, 'c')
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return false when text does not end with search', () => {
+        const result = subject.endsWith(text, 'b')
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+    })
+
+    describe('with offset', () => {
+      test('should return true when offset text ends with search', () => {
+        const result = subject.endsWith(text, 'b', 2)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return true when offset text ends with search (multi-char)', () => {
+        const result = subject.endsWith(text, 'bc', 3)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return false when offset string does not end with search', () => {
+        const result = subject.endsWith(text, 'c', 1)
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+    })
+
+    describe('with bad offset', () => {
+      test('should return false when the offset is negative', () => {
+        const result = subject.endsWith(text, 'a', -1)
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+      test('should return true when the end matches and offset is greater than text length', () => {
+        const result = subject.endsWith(text, 'c', 10)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+    })
+  })
+
+  describe('includes', () => {
+    const text = 'abcde'
+
+    describe('without offset', () => {
+      test('should return true when text contains search', () => {
+        const result = subject.includes(text, 'bcd')
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return false when text does not end with search', () => {
+        const result = subject.includes(text, 'hello')
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+    })
+
+    describe('with offset', () => {
+      test('should return true when offset text does contain search', () => {
+        const result = subject.includes(text, 'c', 1)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return true when offset text does contain search (multi-char)', () => {
+        const result = subject.includes(text, 'bcd', 1)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return false when offset string does not contain search', () => {
+        const result = subject.includes(text, 'abc', 3)
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+    })
+
+    describe('with bad offset', () => {
+      test('should ignore offset when the offset is negative', () => {
+        const result = subject.includes(text, 'a', -100)
+        expect(result).toEqual(true)
+        type test = Expect<Equal<typeof result, true>>
+      })
+      test('should return false when text contains search but offset is greater than text length', () => {
+        const result = subject.includes(text, 'c', 10)
+        expect(result).toEqual(false)
+        type test = Expect<Equal<typeof result, false>>
+      })
+    })
+  })
+
   describe('join', () => {
     test('should join words in both type level and runtime level', () => {
       const result = subject.join(['a', 'b', 'c'], '-')
@@ -284,14 +381,16 @@ describe('primitives', () => {
   })
 
   describe('startsWith', () => {
+    const text = 'abc'
+
     describe('without offset', () => {
       test('should return true when text starts with search', () => {
-        const result = subject.startsWith('abc', 'a')
+        const result = subject.startsWith(text, 'a')
         expect(result).toEqual(true)
         type test = Expect<Equal<typeof result, true>>
       })
       test('should return false when text does not start with search', () => {
-        const result = subject.startsWith('abc', 'b')
+        const result = subject.startsWith(text, 'b')
         expect(result).toEqual(false)
         type test = Expect<Equal<typeof result, false>>
       })
@@ -299,12 +398,12 @@ describe('primitives', () => {
 
     describe('with offset', () => {
       test('should return true when offset text starts with search', () => {
-        const result = subject.startsWith('abc', 'b', 1)
+        const result = subject.startsWith(text, 'b', 1)
         expect(result).toEqual(true)
         type test = Expect<Equal<typeof result, true>>
       })
       test('should return false when offset string does not start with search', () => {
-        const result = subject.startsWith('abc', 'a', 1)
+        const result = subject.startsWith(text, 'a', 1)
         expect(result).toEqual(false)
         type test = Expect<Equal<typeof result, false>>
       })
@@ -312,61 +411,15 @@ describe('primitives', () => {
 
     describe('with bad offset', () => {
       test('should return true when text starts with search and offset is negative', () => {
-        const result = subject.startsWith('abc', 'a', -1)
+        const result = subject.startsWith(text, 'a', -1)
         expect(result).toEqual(true)
         type test = Expect<Equal<typeof result, true>>
       })
       test('should return false when offset is greater than text length', () => {
-        const result = subject.startsWith('abc', 'a', 10)
-        expect(result).toEqual(false)
-        type test = Expect<Equal<typeof result, false>>
-      })
-    })
-  })
-
-  describe('endsWith', () => {
-    describe('without offset', () => {
-      test('should return true when text ends with search', () => {
-        const result = subject.endsWith('abc', 'c')
-        expect(result).toEqual(true)
-        type test = Expect<Equal<typeof result, true>>
-      })
-      test('should return false when text does not end with search', () => {
-        const result = subject.endsWith('abc', 'b')
-        expect(result).toEqual(false)
-        type test = Expect<Equal<typeof result, false>>
-      })
-    })
-
-    describe('with offset', () => {
-      test('should return true when offset text ends with search', () => {
-        const result = subject.endsWith('abc', 'b', 2)
-        expect(result).toEqual(true)
-        type test = Expect<Equal<typeof result, true>>
-      })
-      test('should return true when offset text ends with search (multi-char)', () => {
-        const result = subject.endsWith('abc', 'bc', 3)
-        expect(result).toEqual(true)
-        type test = Expect<Equal<typeof result, true>>
-      })
-      test('should return false when offset string does not end with search', () => {
-        const result = subject.endsWith('abc', 'c', 1)
-        expect(result).toEqual(false)
-        type test = Expect<Equal<typeof result, false>>
-      })
-    })
-
-    describe('with bad offset', () => {
-      test('should return false when the offset is negative', () => {
-        const result = subject.endsWith('abc', 'a', -1)
+        const result = subject.startsWith(text, 'a', 10)
         expect(result).toEqual(false)
         type test = Expect<Equal<typeof result, false>>
       })
-      test('should return true when the end matches and offset is greater than text length', () => {
-        const result = subject.endsWith('abc', 'c', 10)
-        expect(result).toEqual(true)
-        type test = Expect<Equal<typeof result, true>>
-      })
     })
   })
 
diff --git a/src/primitives.ts b/src/primitives.ts
index d8fbf75..1dc0c99 100644
--- a/src/primitives.ts
+++ b/src/primitives.ts
@@ -1,5 +1,5 @@
 import type { Math } from './math'
-import { TupleOf } from './utils'
+import type { TupleOf } from './utils'
 
 /**
  * Gets the character at the given index.
@@ -372,6 +372,40 @@ function startsWith<T extends string, S extends string, P extends number = 0>(
   return text.startsWith(search, position) as StartsWith<T, S, P>
 }
 
+/**
+ * Checks if a string includes another string.
+ * T: The string to check.
+ * S: The string to check against.
+ * P: The position to start the search.
+ */
+type Includes<
+  T extends string,
+  S extends string,
+  P extends number = 0,
+> = Math.IsNegative<P> extends false
+  ? P extends 0
+    ? T extends `${string}${S}${string}`
+      ? true
+      : false
+    : Includes<Slice<T, P>, S, 0> // P is >0, slice
+  : Includes<T, S, 0> // P is negative, ignore it
+
+/**
+ * A strongly-typed version of `String.prototype.includes`.
+ * @param text the string to search
+ * @param search the string to search with
+ * @param position the index to start search at
+ * @returns boolean, whether or not the text contains the search string.
+ * @example includes('abcde', 'bcd') // true
+ */
+function includes<T extends string, S extends string, P extends number = 0>(
+  text: T,
+  search: S,
+  position = 0 as P,
+) {
+  return text.includes(search, position) as Includes<T, S, P>
+}
+
 /**
  * Trims all whitespaces at the start of a string.
  * T: The string to trim.
@@ -424,6 +458,7 @@ export type {
   CharAt,
   Concat,
   EndsWith,
+  Includes,
   Join,
   Length,
   PadEnd,
@@ -442,6 +477,7 @@ export {
   charAt,
   concat,
   endsWith,
+  includes,
   join,
   length,
   padEnd,