diff --git a/README.md b/README.md
index eb37991..e7fb5ed 100644
--- a/README.md
+++ b/README.md
@@ -208,6 +208,7 @@ Challenges, solutions, and unit tests are presented in the form of **IPython/Jup
 | Implement breadth-first search on a tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_bfs/bfs_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_bfs/bfs_solution.ipynb) |
 | Determine the height of a tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_height/height_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_height/height_solution.ipynb) |
 | Implement a graph | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph/graph_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph/graph_solution.ipynb) |
+| Implement depth-first search on a graph |  [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_solution.ipynb) |
 | Print a tree using pre-order traversal without recursion | [Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md)│[Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md) |
 | Determine the lowest common ancestor of two nodes | [Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md)│[Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md) |
 | Transform a binary tree into a heap | [Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md)│[Contribute](https://github.com/donnemartin/interactive-coding-challenges/blob/master/CONTRIBUTING.md) |
diff --git a/graphs_trees/graph_dfs/__init__.py b/graphs_trees/graph_dfs/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/graphs_trees/graph_dfs/dfs_challenge.ipynb b/graphs_trees/graph_dfs/dfs_challenge.ipynb
new file mode 100644
index 0000000..a8fa189
--- /dev/null
+++ b/graphs_trees/graph_dfs/dfs_challenge.ipynb
@@ -0,0 +1,209 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement depth-first search on a graph.\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "\n",
+    "* Is the graph directed?\n",
+    "    * Yes\n",
+    "* Can we assume we already have Graph and Node classes?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "Input:\n",
+    "* `add_edge(source, destination, weight)`\n",
+    "\n",
+    "```\n",
+    "graph.add_edge(0, 1, 5)\n",
+    "graph.add_edge(0, 4, 3)\n",
+    "graph.add_edge(0, 5, 2)\n",
+    "graph.add_edge(1, 3, 5)\n",
+    "graph.add_edge(1, 4, 4)\n",
+    "graph.add_edge(2, 1, 6)\n",
+    "graph.add_edge(3, 2, 7)\n",
+    "graph.add_edge(3, 4, 8)\n",
+    "```\n",
+    "\n",
+    "Result:\n",
+    "* Order of nodes visited: [0, 1, 3, 2, 4, 5]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_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": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../graph/graph.py\n",
+    "%load ../graph/graph.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def dfs(root, visit_func):\n",
+    "    # TODO: Implement me\n",
+    "    pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**The following unit test is expected to fail until you solve the challenge.**"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../utils/results.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# %load test_dfs.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestDfs(object):\n",
+    "\n",
+    "    def __init__(self):\n",
+    "        self.results = Results()\n",
+    "\n",
+    "    def test_dfs(self):\n",
+    "        nodes = []\n",
+    "        graph = Graph()\n",
+    "        for id in range(0, 6):\n",
+    "            nodes.append(graph.add_node(id))\n",
+    "        graph.add_edge(0, 1, 5)\n",
+    "        graph.add_edge(0, 4, 3)\n",
+    "        graph.add_edge(0, 5, 2)\n",
+    "        graph.add_edge(1, 3, 5)\n",
+    "        graph.add_edge(1, 4, 4)\n",
+    "        graph.add_edge(2, 1, 6)\n",
+    "        graph.add_edge(3, 2, 7)\n",
+    "        graph.add_edge(3, 4, 8)\n",
+    "        dfs(nodes[0], self.results.add_result)\n",
+    "        assert_equal(str(self.results), \"[0, 1, 3, 2, 4, 5]\")\n",
+    "\n",
+    "        print('Success: test_dfs')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestDfs()\n",
+    "    test.test_dfs()\n",
+    "\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/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_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/graphs_trees/graph_dfs/dfs_solution.ipynb b/graphs_trees/graph_dfs/dfs_solution.ipynb
new file mode 100644
index 0000000..ff497d5
--- /dev/null
+++ b/graphs_trees/graph_dfs/dfs_solution.ipynb
@@ -0,0 +1,231 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement depth-first search on a graph.\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "\n",
+    "* Is the graph directed?\n",
+    "    * Yes\n",
+    "* Can we assume we already have Graph and Node classes?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "Input:\n",
+    "* `add_edge(source, destination, weight)`\n",
+    "\n",
+    "```\n",
+    "graph.add_edge(0, 1, 5)\n",
+    "graph.add_edge(0, 4, 3)\n",
+    "graph.add_edge(0, 5, 2)\n",
+    "graph.add_edge(1, 3, 5)\n",
+    "graph.add_edge(1, 4, 4)\n",
+    "graph.add_edge(2, 1, 6)\n",
+    "graph.add_edge(3, 2, 7)\n",
+    "graph.add_edge(3, 4, 8)\n",
+    "```\n",
+    "\n",
+    "Result:\n",
+    "* Order of nodes visited: [0, 1, 3, 2, 4, 5]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "If we want to visit every node in a graph, we generally prefer depth-first search since it is simpler (no need to use a queue).  For shortest path, we generally use breadth-first search.\n",
+    "\n",
+    "* Visit the current node and mark it visited\n",
+    "* Iterate through each adjacent node\n",
+    "    * If the node has not been visited, call dfs on it\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(V + E), where V = number of vertices and E = number of edges\n",
+    "* Space: O(V + E)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../graph/graph.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def dfs(root, visit_func):\n",
+    "    if root is None:\n",
+    "        return\n",
+    "    visit_func(root.id)\n",
+    "    root.visited = True\n",
+    "    for node in root.adjacent:\n",
+    "        if not node.visited:\n",
+    "            dfs(node, visit_func)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../utils/results.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_dfs.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_dfs.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestDfs(object):\n",
+    "\n",
+    "    def __init__(self):\n",
+    "        self.results = Results()\n",
+    "\n",
+    "    def test_dfs(self):\n",
+    "        nodes = []\n",
+    "        graph = Graph()\n",
+    "        for id in range(0, 6):\n",
+    "            nodes.append(graph.add_node(id))\n",
+    "        graph.add_edge(0, 1, 5)\n",
+    "        graph.add_edge(0, 4, 3)\n",
+    "        graph.add_edge(0, 5, 2)\n",
+    "        graph.add_edge(1, 3, 5)\n",
+    "        graph.add_edge(1, 4, 4)\n",
+    "        graph.add_edge(2, 1, 6)\n",
+    "        graph.add_edge(3, 2, 7)\n",
+    "        graph.add_edge(3, 4, 8)\n",
+    "        dfs(nodes[0], self.results.add_result)\n",
+    "        assert_equal(str(self.results), \"[0, 1, 3, 2, 4, 5]\")\n",
+    "\n",
+    "        print('Success: test_dfs')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestDfs()\n",
+    "    test.test_dfs()\n",
+    "\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_dfs\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_dfs.py"
+   ]
+  }
+ ],
+ "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/graphs_trees/graph_dfs/test_dfs.py b/graphs_trees/graph_dfs/test_dfs.py
new file mode 100644
index 0000000..2830387
--- /dev/null
+++ b/graphs_trees/graph_dfs/test_dfs.py
@@ -0,0 +1,34 @@
+from nose.tools import assert_equal
+
+
+class TestDfs(object):
+
+    def __init__(self):
+        self.results = Results()
+
+    def test_dfs(self):
+        nodes = []
+        graph = Graph()
+        for id in range(0, 6):
+            nodes.append(graph.add_node(id))
+        graph.add_edge(0, 1, 5)
+        graph.add_edge(0, 4, 3)
+        graph.add_edge(0, 5, 2)
+        graph.add_edge(1, 3, 5)
+        graph.add_edge(1, 4, 4)
+        graph.add_edge(2, 1, 6)
+        graph.add_edge(3, 2, 7)
+        graph.add_edge(3, 4, 8)
+        dfs(nodes[0], self.results.add_result)
+        assert_equal(str(self.results), "[0, 1, 3, 2, 4, 5]")
+
+        print('Success: test_dfs')
+
+
+def main():
+    test = TestDfs()
+    test.test_dfs()
+
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file