diff --git a/stacks_queues/stack/__init__.py b/stacks_queues/stack/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/stacks_queues/stack/stack.py b/stacks_queues/stack/stack.py
index e1a9ddb..82b74a7 100644
--- a/stacks_queues/stack/stack.py
+++ b/stacks_queues/stack/stack.py
@@ -1,10 +1,11 @@
-
 class Node(object):
+    
     def __init__(self, data):
         self.data = data
         self.next = None
 
 class Stack(object):
+    
     def __init__(self, top=None):
         self.top = top
 
diff --git a/stacks_queues/stack/stack_challenge.ipynb b/stacks_queues/stack/stack_challenge.ipynb
new file mode 100644
index 0000000..af604cb
--- /dev/null
+++ b/stacks_queues/stack/stack_challenge.ipynb
@@ -0,0 +1,218 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement a stack with push, pop, peek, and is_empty methods using a linked list.\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)\n",
+    "* [Pythonic-Code](#Pythonic-Code)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "\n",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* None"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "### Push\n",
+    "\n",
+    "* Push to empty stack\n",
+    "* Push to non-empty stack\n",
+    "\n",
+    "### Pop\n",
+    "\n",
+    "* Pop on empty stack\n",
+    "* Pop on single element stack\n",
+    "* Pop on multiple element stack\n",
+    "\n",
+    "### Peek\n",
+    "\n",
+    "* Peek on empty stack\n",
+    "* Peek on one or more element stack\n",
+    "\n",
+    "### Is Empty\n",
+    "\n",
+    "* Is empty on empty stack\n",
+    "* Is empty on one or more element stack"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/stacks_queues/stack/stack_solution.ipynb).  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "class Node(object):\n",
+    "    \n",
+    "    def __init__(self, data):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "class Stack(object):\n",
+    "    \n",
+    "    def __init__(self, top=None):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def push(self, data):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def pop(self):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def peek(self):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def is_empty(self):\n",
+    "        # TODO: Implement me\n",
+    "        pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test\n",
+    "\n",
+    "\n",
+    "\n",
+    "**The following unit test is expected to fail until you solve the challenge.**"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# %load test_stack.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestStack(object):\n",
+    "    \n",
+    "    # TODO: It would be better if we had unit tests for each\n",
+    "    # method in addition to the following end-to-end test\n",
+    "    def test_end_to_end(self):\n",
+    "        print('Test: Empty stack')\n",
+    "        stack = Stack()\n",
+    "        assert_equal(stack.peek(), None)\n",
+    "        assert_equal(stack.pop(), None)\n",
+    "\n",
+    "        print('Test: One element')\n",
+    "        top = Node(5)\n",
+    "        stack = Stack(top)\n",
+    "        assert_equal(stack.pop(), 5)\n",
+    "        assert_equal(stack.peek(), None)\n",
+    "\n",
+    "        print('Test: More than one element')\n",
+    "        stack = Stack()\n",
+    "        stack.push(1)\n",
+    "        stack.push(2)\n",
+    "        stack.push(3)\n",
+    "        assert_equal(stack.pop(), 3)\n",
+    "        assert_equal(stack.peek(), 2)\n",
+    "        assert_equal(stack.pop(), 2)\n",
+    "        assert_equal(stack.peek(), 1)\n",
+    "        assert_equal(stack.is_empty(), False)\n",
+    "        assert_equal(stack.pop(), 1)\n",
+    "        assert_equal(stack.peek(), None)\n",
+    "        assert_equal(stack.is_empty(), True)\n",
+    "        \n",
+    "        print('Success: test_end_to_end')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestStack()\n",
+    "    test.test_end_to_end()\n",
+    "    \n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/stacks_queues/stack/stack_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.10"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/stacks_queues/stack/stack_solution.ipynb b/stacks_queues/stack/stack_solution.ipynb
index fb147cf..91ba17c 100644
--- a/stacks_queues/stack/stack_solution.ipynb
+++ b/stacks_queues/stack/stack_solution.ipynb
@@ -4,7 +4,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
    ]
   },
   {
@@ -27,7 +34,7 @@
    "source": [
     "## Constraints\n",
     "\n",
-    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
     "* None"
    ]
@@ -130,13 +137,14 @@
    ],
    "source": [
     "%%writefile stack.py\n",
-    "\n",
     "class Node(object):\n",
+    "    \n",
     "    def __init__(self, data):\n",
     "        self.data = data\n",
     "        self.next = None\n",
     "\n",
     "class Stack(object):\n",
+    "    \n",
     "    def __init__(self, top=None):\n",
     "        self.top = top\n",
     "\n",
@@ -177,8 +185,7 @@
    "metadata": {},
    "source": [
     "## Unit Test\n",
-    "\n",
-    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
+    "\n"
    ]
   },
   {
@@ -192,17 +199,17 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Test: Empty stack\n",
-      "Test: One element\n",
-      "Test: More than one element\n",
-      "Success: test_end_to_end\n"
+      "Overwriting test_stack.py\n"
      ]
     }
    ],
    "source": [
+    "%%writefile test_stack.py\n",
     "from nose.tools import assert_equal\n",
     "\n",
-    "class Test(object):\n",
+    "\n",
+    "class TestStack(object):\n",
+    "    \n",
     "    # TODO: It would be better if we had unit tests for each\n",
     "    # method in addition to the following end-to-end test\n",
     "    def test_end_to_end(self):\n",
@@ -233,9 +240,34 @@
     "        \n",
     "        print('Success: test_end_to_end')\n",
     "\n",
+    "def main():\n",
+    "    test = TestStack()\n",
+    "    test.test_end_to_end()\n",
+    "    \n",
     "if __name__ == '__main__':\n",
-    "    test = Test()\n",
-    "    test.test_end_to_end()"
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Test: Empty stack\n",
+      "Test: One element\n",
+      "Test: More than one element\n",
+      "Success: test_end_to_end\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_stack.py"
    ]
   },
   {
diff --git a/stacks_queues/stack/test_stack.py b/stacks_queues/stack/test_stack.py
new file mode 100644
index 0000000..cc56e2e
--- /dev/null
+++ b/stacks_queues/stack/test_stack.py
@@ -0,0 +1,41 @@
+from nose.tools import assert_equal
+
+
+class TestStack(object):
+    
+    # TODO: It would be better if we had unit tests for each
+    # method in addition to the following end-to-end test
+    def test_end_to_end(self):
+        print('Test: Empty stack')
+        stack = Stack()
+        assert_equal(stack.peek(), None)
+        assert_equal(stack.pop(), None)
+
+        print('Test: One element')
+        top = Node(5)
+        stack = Stack(top)
+        assert_equal(stack.pop(), 5)
+        assert_equal(stack.peek(), None)
+
+        print('Test: More than one element')
+        stack = Stack()
+        stack.push(1)
+        stack.push(2)
+        stack.push(3)
+        assert_equal(stack.pop(), 3)
+        assert_equal(stack.peek(), 2)
+        assert_equal(stack.pop(), 2)
+        assert_equal(stack.peek(), 1)
+        assert_equal(stack.is_empty(), False)
+        assert_equal(stack.pop(), 1)
+        assert_equal(stack.peek(), None)
+        assert_equal(stack.is_empty(), True)
+        
+        print('Success: test_end_to_end')
+
+def main():
+    test = TestStack()
+    test.test_end_to_end()
+    
+if __name__ == '__main__':
+    main()
\ No newline at end of file