diff --git a/implementations/join.js b/implementations/join.js
new file mode 100644
index 0000000..082a49d
--- /dev/null
+++ b/implementations/join.js
@@ -0,0 +1,62 @@
+/**
+  *
+  MDN Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join
+
+  The join() method concats every element in array
+  with a defined separator and returns a new string.
+
+  Example 1 - Without a separator as parameter:
+  ['a', 'e', 'i', 'o', 'u'].join();
+  must return:
+  'a,e,i,o,u'
+
+  Example 2 - With a undefined as parameter:
+  ['a', 'e', 'i', 'o', 'u'].join(undefined);
+  must return:
+  'a,e,i,o,u'
+
+  Example 3 - With a empty string as parameter
+  ['a', 'e', 'i', 'o', 'u'].join('');
+  must return:
+  'aeiou'
+
+  Example 4 - With a string as parameter
+  ['a', 'e', 'i', 'o', 'u'].join('-');
+  must return:
+  'a-e-i-o-u'
+
+  Example 5 - With a function as parameter
+  ['a', 'e', 'i', 'o', 'u'].join(() => {});
+  must return:
+  'a() => {}e() => {}i() => {}o() => {}u'
+
+  Example 6 - With a object as parameter
+  ['a', 'e', 'i', 'o', 'u'].join({});
+  must return:
+  'a[object Object]e[object Object]i[object Object]o[object Object]u'
+
+  Example 7 - With an array as parameter
+  ['a', 'e', 'i', 'o', 'u'].join([1, 2, 3]);
+  must return:
+  'a1,2,3e1,2,3i1,2,3o1,2,3u'
+
+  Example 8 - With a boolean as parameter
+  ['a', 'e', 'i', 'o', 'u'].join(true);
+  must return:
+  'atrueetrueitrueotrueu'
+ */
+
+Array.prototype.join = function join(separator) {
+  let returnValue = '';
+  let sep = separator;
+
+  if (Object.prototype.toString.call(sep) === '[object Undefined]') {
+    sep = ',';
+  }
+
+  for (let index = 0; index < this.length; index += 1) {
+    returnValue += this[index] + (index < this.length - 1 ? sep : '');
+  }
+
+  return returnValue;
+};
diff --git a/implementations/join.spec.js b/implementations/join.spec.js
new file mode 100644
index 0000000..26c94a3
--- /dev/null
+++ b/implementations/join.spec.js
@@ -0,0 +1,53 @@
+require('./join');
+
+describe('join', () => {
+  const data = ['a', 'e', 'i', 'o', 'u'];
+
+  describe('when doesn\'t pass parameters', () => {
+    test('return \'a,e,i,o,u\'', () => {
+      expect(data.join()).toBe('a,e,i,o,u');
+    });
+  });
+
+  describe('when pass \'undefined\' as parameter', () => {
+    test('return \'a,e,i,o,u\'', () => {
+      expect(data.join(undefined)).toBe('a,e,i,o,u');
+    });
+  });
+
+  describe('when pass \'\' as parameter', () => {
+    test('return \'aeiou\'', () => {
+      expect(data.join('')).toBe('aeiou');
+    });
+  });
+
+  describe('when pass a string as parameter', () => {
+    test('return \'a-e-i-o-u\'', () => {
+      expect(data.join('-')).toBe('a-e-i-o-u');
+    });
+  });
+
+  describe('when pass a function as parameter', () => {
+    test('return \'a() => {}e() => {}i() => {}o() => {}u\'', () => {
+      expect(data.join(() => {})).toBe('a() => {}e() => {}i() => {}o() => {}u');
+    });
+  });
+
+  describe('when pass a object as parameter', () => {
+    test('return \'a[object Object]e[object Object]i[object Object]o[object Object]u\'', () => {
+      expect(data.join({})).toBe('a[object Object]e[object Object]i[object Object]o[object Object]u');
+    });
+  });
+
+  describe('when pass an array as parameter', () => {
+    test('return \'a1,2,3e1,2,3i1,2,3o1,2,3u\'', () => {
+      expect(data.join([1, 2, 3])).toBe('a1,2,3e1,2,3i1,2,3o1,2,3u');
+    });
+  });
+
+  describe('when pass a boolean as parameter', () => {
+    test('return \'atrueetrueitrueotrueu\'', () => {
+      expect(data.join(true)).toBe('atrueetrueitrueotrueu');
+    });
+  });
+});