diff --git a/solutions/object_oriented_design/call_center/__init__.py b/solutions/object_oriented_design/call_center/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/solutions/object_oriented_design/call_center/call_center.ipynb b/solutions/object_oriented_design/call_center/call_center.ipynb
new file mode 100644
index 0000000..deac342
--- /dev/null
+++ b/solutions/object_oriented_design/call_center/call_center.ipynb
@@ -0,0 +1,206 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/system-design-primer-primer)."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Design a call center"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints and assumptions\n",
+    "\n",
+    "* What levels of employees are in the call center?\n",
+    "    * Operator, supervisor, director\n",
+    "* Can we assume operators always get the initial calls?\n",
+    "    * Yes\n",
+    "* If there is no free operators or the operator can't handle the call, does the call go to the supervisors?\n",
+    "    * Yes\n",
+    "* If there is no free supervisors or the supervisor can't handle the call, does the call go to the directors?\n",
+    "    * Yes\n",
+    "* Can we assume the directors can handle all calls?\n",
+    "    * Yes\n",
+    "* What happens if nobody can answer the call?\n",
+    "    * It gets queued\n",
+    "* Do we need to handle 'VIP' calls where we put someone to the front of the line?\n",
+    "    * No\n",
+    "* Can we assume inputs are valid or do we have to validate them?\n",
+    "    * Assume they're valid"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting call_center.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile call_center.py\n",
+    "from abc import ABCMeta, abstractmethod\n",
+    "from collections import deque\n",
+    "from enum import Enum\n",
+    "\n",
+    "\n",
+    "class Rank(Enum):\n",
+    "\n",
+    "    OPERATOR = 0\n",
+    "    SUPERVISOR = 1\n",
+    "    DIRECTOR = 2\n",
+    "\n",
+    "\n",
+    "class Employee(metaclass=ABCMeta):\n",
+    "\n",
+    "    def __init__(self, employee_id, name, rank, call_center):\n",
+    "        self.employee_id = employee_id\n",
+    "        self.name = name\n",
+    "        self.rank = rank\n",
+    "        self.call = None\n",
+    "        self.call_center = call_center\n",
+    "\n",
+    "    def take_call(self, call):\n",
+    "        \"\"\"Assume the employee will always successfully take the call.\"\"\"\n",
+    "        self.call = call\n",
+    "        self.call.employee = self\n",
+    "        self.call.state = CallState.IN_PROGRESS\n",
+    "\n",
+    "    def complete_call(self):\n",
+    "        self.call.state = CallState.COMPLETE\n",
+    "        self.call_center.notify_call_completed(self.call)\n",
+    "\n",
+    "    @abstractmethod\n",
+    "    def escalate_call(self):\n",
+    "        pass\n",
+    "\n",
+    "    def _escalate_call(self):\n",
+    "        self.call.state = CallState.READY\n",
+    "        call = self.call\n",
+    "        self.call = None\n",
+    "        self.call_center.notify_call_escalated(call)\n",
+    "\n",
+    "\n",
+    "class Operator(Employee):\n",
+    "\n",
+    "    def __init__(self, employee_id, name):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR)\n",
+    "\n",
+    "    def escalate_call(self):\n",
+    "        self.call.level = Rank.SUPERVISOR\n",
+    "        self._escalate_call()\n",
+    "\n",
+    "\n",
+    "class Supervisor(Employee):\n",
+    "\n",
+    "    def __init__(self, employee_id, name):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR)\n",
+    "\n",
+    "    def escalate_call(self):\n",
+    "        self.call.level = Rank.DIRECTOR\n",
+    "        self._escalate_call()\n",
+    "\n",
+    "\n",
+    "class Director(Employee):\n",
+    "\n",
+    "    def __init__(self, employee_id, name):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR)\n",
+    "\n",
+    "    def escalate_call(self):\n",
+    "        raise NotImplemented('Directors must be able to handle any call')\n",
+    "\n",
+    "\n",
+    "class CallState(Enum):\n",
+    "\n",
+    "    READY = 0\n",
+    "    IN_PROGRESS = 1\n",
+    "    COMPLETE = 2\n",
+    "\n",
+    "\n",
+    "class Call(object):\n",
+    "\n",
+    "    def __init__(self, rank):\n",
+    "        self.state = CallState.READY\n",
+    "        self.rank = rank\n",
+    "        self.employee = None\n",
+    "\n",
+    "\n",
+    "class CallCenter(object):\n",
+    "\n",
+    "    def __init__(self, operators, supervisors, directors):\n",
+    "        self.operators = operators\n",
+    "        self.supervisors = supervisors\n",
+    "        self.directors = directors\n",
+    "        self.queued_calls = deque()\n",
+    "\n",
+    "    def dispatch_call(self, call):\n",
+    "        if call.rank not in (Rank.OPERATOR, Rank.SUPERVISOR, Rank.DIRECTOR):\n",
+    "            raise ValueError('Invalid call rank: {}'.format(call.rank))\n",
+    "        employee = None\n",
+    "        if call.rank == Rank.OPERATOR:\n",
+    "            employee = self._dispatch_call(call, self.operators)\n",
+    "        if call.rank == Rank.SUPERVISOR or employee is None:\n",
+    "            employee = self._dispatch_call(call, self.supervisors)\n",
+    "        if call.rank == Rank.DIRECTOR or employee is None:\n",
+    "            employee = self._dispatch_call(call, self.directors)\n",
+    "        if employee is None:\n",
+    "            self.queued_calls.append(call)\n",
+    "\n",
+    "    def _dispatch_call(self, call, employees):\n",
+    "        for employee in employees:\n",
+    "            if employee.call is None:\n",
+    "                employee.take_call(call)\n",
+    "                return employee\n",
+    "        return None\n",
+    "\n",
+    "    def notify_call_escalated(self, call):  # ...\n",
+    "    def notify_call_completed(self, call):  # ...\n",
+    "    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):  # ..."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/solutions/object_oriented_design/call_center/call_center.py b/solutions/object_oriented_design/call_center/call_center.py
new file mode 100644
index 0000000..7bdd992
--- /dev/null
+++ b/solutions/object_oriented_design/call_center/call_center.py
@@ -0,0 +1,117 @@
+from abc import ABCMeta, abstractmethod
+from collections import deque
+from enum import Enum
+
+
+class Rank(Enum):
+
+    OPERATOR = 0
+    SUPERVISOR = 1
+    DIRECTOR = 2
+
+
+class Employee(metaclass=ABCMeta):
+
+    def __init__(self, employee_id, name, rank, call_center):
+        self.employee_id = employee_id
+        self.name = name
+        self.rank = rank
+        self.call = None
+        self.call_center = call_center
+
+    def take_call(self, call):
+        """Assume the employee will always successfully take the call."""
+        self.call = call
+        self.call.employee = self
+        self.call.state = CallState.IN_PROGRESS
+
+    def complete_call(self):
+        self.call.state = CallState.COMPLETE
+        self.call_center.notify_call_completed(self.call)
+
+    @abstractmethod
+    def escalate_call(self):
+        pass
+
+    def _escalate_call(self):
+        self.call.state = CallState.READY
+        call = self.call
+        self.call = None
+        self.call_center.notify_call_escalated(call)
+
+
+class Operator(Employee):
+
+    def __init__(self, employee_id, name):
+        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR)
+
+    def escalate_call(self):
+        self.call.level = Rank.SUPERVISOR
+        self._escalate_call()
+
+
+class Supervisor(Employee):
+
+    def __init__(self, employee_id, name):
+        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR)
+
+    def escalate_call(self):
+        self.call.level = Rank.DIRECTOR
+        self._escalate_call()
+
+
+class Director(Employee):
+
+    def __init__(self, employee_id, name):
+        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR)
+
+    def escalate_call(self):
+        raise NotImplemented('Directors must be able to handle any call')
+
+
+class CallState(Enum):
+
+    READY = 0
+    IN_PROGRESS = 1
+    COMPLETE = 2
+
+
+class Call(object):
+
+    def __init__(self, rank):
+        self.state = CallState.READY
+        self.rank = rank
+        self.employee = None
+
+
+class CallCenter(object):
+
+    def __init__(self, operators, supervisors, directors):
+        self.operators = operators
+        self.supervisors = supervisors
+        self.directors = directors
+        self.queued_calls = deque()
+
+    def dispatch_call(self, call):
+        if call.rank not in (Rank.OPERATOR, Rank.SUPERVISOR, Rank.DIRECTOR):
+            raise ValueError('Invalid call rank: {}'.format(call.rank))
+        employee = None
+        if call.rank == Rank.OPERATOR:
+            employee = self._dispatch_call(call, self.operators)
+        if call.rank == Rank.SUPERVISOR or employee is None:
+            employee = self._dispatch_call(call, self.supervisors)
+        if call.rank == Rank.DIRECTOR or employee is None:
+            employee = self._dispatch_call(call, self.directors)
+        if employee is None:
+            self.queued_calls.append(call)
+
+    def _dispatch_call(self, call, employees):
+        for employee in employees:
+            if employee.call is None:
+                employee.take_call(call)
+                return employee
+        return None
+
+    def notify_call_escalated(self, call):  # ...
+    def notify_call_completed(self, call):  # ...
+    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):  # ...
\ No newline at end of file