diff --git a/CONTRACT.md b/CONTRACT.md
index 831bfbc..5b01d97 100644
--- a/CONTRACT.md
+++ b/CONTRACT.md
@@ -32,12 +32,12 @@ Complete **ONLY** the [Classic](https://github.com/GuildCrafts/core-algorithms/b
 - [x] Tests for `fizzBuzz()` exist.
 - [x] `isPalindrome()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
 - [x] Tests for `isPalindrome()` exist with at least 2 unit tests using valid inputs.
-- [ ] `factorial()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `factorial()` exist with at least 2 unit tests using valid inputs.
-- [ ] `fibonacci()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `fibonacci()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
-- [ ] `collatzConjecture()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `collatzConjecture()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `factorial()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `factorial()` exist with at least 2 unit tests using valid inputs.
+- [x] `fibonacci()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `fibonacci()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `collatzConjecture()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `collatzConjecture()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
 - [ ] `setUnion()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
 - [ ] Tests for `setUnion()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
 - [ ] `setIntersection()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
diff --git a/src/collatzConjecture.js b/src/collatzConjecture.js
new file mode 100644
index 0000000..3f5a5e1
--- /dev/null
+++ b/src/collatzConjecture.js
@@ -0,0 +1,32 @@
+// collatzConjecture
+//
+// Return the Collatz sequence for a given number.
+//
+// The Collatz sequence for any positive integer n is defined as follows:
+//
+// If n is even, divide it by 2 to get n / 2. If n is odd, multiply it by 3 and add 1 to obtain 3n + 1. Repeat the process until you reach 1.
+// collatzConjecture(1)
+// // => [1]
+//
+// collatzConjecture(7)
+// // => [7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
+
+
+export default function collatzConjecture(num) {
+  if (!Number.isInteger(num) || num < 0) {
+    throw new Error('Invalid input format. Expected a positive integer')
+  }
+  let collatzArr = [num]
+  let result = num
+
+  while (result > 1) {
+    if (result % 2 === 0) {
+      result = result / 2
+      collatzArr.push(result)
+    } else {
+      result = (result * 3) + 1
+      collatzArr.push(result)
+    }
+  }
+  return collatzArr
+}
diff --git a/src/factorial.js b/src/factorial.js
new file mode 100644
index 0000000..cb8372f
--- /dev/null
+++ b/src/factorial.js
@@ -0,0 +1,16 @@
+// factorial
+//
+// Return the factorial of a number.
+//
+// factorial(5)
+// // => 120
+
+export default function factorial(num) {
+  var factorialElements = [num]
+  for (var i = num; i > 1; i--) {
+  factorialElements.push(i - 1)
+  }
+  return factorialElements.reduce(function(a,b){
+  return a*b
+  }, 1)
+}
diff --git a/src/fibonacci.js b/src/fibonacci.js
new file mode 100644
index 0000000..88a9a4a
--- /dev/null
+++ b/src/fibonacci.js
@@ -0,0 +1,24 @@
+// fibonacci
+//
+// Return an array of Fibonacci numbers to the nth position.
+//
+// fibonacci(10)
+// // => [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+
+export default function fibonacci(num) {
+  if (typeof num !== 'number') {
+    throw new Error('Invalid input format. Expected a number')
+  }
+  var first = 0
+  var second = 1
+  var result
+  var fibonacciArr = [0]
+
+  for (var i = 1; i < num; i++) {
+    result = first + second
+    first = second
+    second = result
+    fibonacciArr.push(first)
+  }
+  return fibonacciArr
+}
diff --git a/test/collatzConjecture_test.js b/test/collatzConjecture_test.js
new file mode 100644
index 0000000..c895ca0
--- /dev/null
+++ b/test/collatzConjecture_test.js
@@ -0,0 +1,18 @@
+import { expect } from 'chai'
+import collatzConjecture from '../src/collatzConjecture'
+
+describe('collatzConjecture()', function(){
+
+  it('should be a function', function(){
+    expect(collatzConjecture).to.be.a('function')
+  })
+  it('returns a Collatz sequence for any positive integer', function(){
+    expect(collatzConjecture(7)).to.eql([7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1])
+    expect(collatzConjecture(3)).to.eql([3, 10, 5, 16, 8, 4, 2, 1])
+  })
+
+  it('throws an error for any invalid inputs', function() {
+    expect(function() {collatzConjecture(-1)}).to.throw('Invalid input format. Expected a positive integer')
+    expect(function() {collatzConjecture('seven')}).to.throw('Invalid input format. Expected a positive integer')
+  })
+})
diff --git a/test/factorial_test.js b/test/factorial_test.js
new file mode 100644
index 0000000..12daa9e
--- /dev/null
+++ b/test/factorial_test.js
@@ -0,0 +1,14 @@
+import { expect } from 'chai'
+import factorial from '../src/factorial'
+
+describe('factorial()', function(){
+
+  it('should be a function', function(){
+    expect(factorial).to.be.a('function')
+  })
+
+  it('returns the factorial of any fiven number', function() {
+    expect(factorial(5)).to.eql(120)
+    expect(factorial(4)).to.eql(24)
+  })
+})
diff --git a/test/fibonacci_test.js b/test/fibonacci_test.js
new file mode 100644
index 0000000..06154f6
--- /dev/null
+++ b/test/fibonacci_test.js
@@ -0,0 +1,18 @@
+import { expect } from 'chai'
+import fibonacci from '../src/fibonacci'
+
+describe ('fibonacci', function(){
+
+  it('should be a function', function() {
+    expect(fibonacci).to.be.a('function')
+  })
+
+  it('returns an array of Fibonacci numbers to the nth position.', function() {
+    expect(fibonacci(10)).to.eql([0, 1, 1, 2, 3, 5, 8, 13, 21, 34])
+    expect(fibonacci(5)).to.eql([0, 1, 1, 2, 3])
+  })
+
+  it('throws an error when given invalid inputs', function() {
+    expect(function() {fibonacci('five') }).to.throw('Invalid input format. Expected a number')
+  })
+})
diff --git a/test/makeChange_test.js b/test/makeChange_test.js
index 2ca1a8a..9956816 100644
--- a/test/makeChange_test.js
+++ b/test/makeChange_test.js
@@ -53,13 +53,13 @@ describe('makeChange()', function(){
 
   it('throws an error when given invalid inputs', function() {
     expect(function(){ makeChange(100, 170) }).to.throw(
-      'Invalid input format. Expected an object literal'
+      'Invalid input format. Expected an object'
     )
   })
 
   it('throws an error when given no arguments', function() {
     expect(function(){ makeChange() }).to.throw(
-      'Invalid input format. Expected an object literal'
+      'Invalid input format. Expected an object'
     )
   })
 })