diff --git a/.clang-format b/.clang-format
index 90d254290..89b87e25d 100644
--- a/.clang-format
+++ b/.clang-format
@@ -3,4 +3,7 @@ DerivePointerAlignment: true
 IndentCaseLabels: false
 PointerAlignment: Right
 SpaceAfterCStyleCast: true
-
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: false
+AllowShortIfStatementsOnASingleLine: false
diff --git a/.travis.yml b/.travis.yml
index 220df4b86..174fee43f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,8 +6,16 @@ matrix:
   include:
     - os: linux
       dist: trusty
+      python: "2.7"
+    - os: linux
+      dist: trusty
+      python: "3.5"
     - os: osx
       osx_image: xcode7
+      python: "2.7"
+    - os: osx
+      osx_image: xcode7
+      python: "3.5"
     - os: linux
       dist: trusty
       env: LINT=1
@@ -22,5 +30,12 @@ matrix:
         - .travis/check-git-clang-format-output.sh
 
 install:
+  - ./install-dependencies.sh
   - make
   - make test
+  - cd lib/python
+  - python setup.py install --user
+  - cd ../..
+
+script:
+  - python test/test.py
diff --git a/install-dependencies.sh b/install-dependencies.sh
new file mode 100755
index 000000000..f84da1684
--- /dev/null
+++ b/install-dependencies.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+ROOT_DIR=$(cd "$(dirname "${BASH_SOURCE:-$0}")"; pwd)
+
+platform="unknown"
+unamestr="$(uname)"
+if [[ "$unamestr" == "Linux" ]]; then
+  echo "Platform is linux."
+  platform="linux"
+elif [[ "$unamestr" == "Darwin" ]]; then
+  echo "Platform is macosx."
+  platform="macosx"
+else
+  echo "Unrecognized platform."
+  exit 1
+fi
+
+if [[ $platform == "linux" ]]; then
+  sudo apt-get update
+  sudo apt-get install -y git python-dev
+fi
diff --git a/lib/python/object_id.c b/lib/python/object_id.c
new file mode 100644
index 000000000..bd7db9bc7
--- /dev/null
+++ b/lib/python/object_id.c
@@ -0,0 +1,91 @@
+#include "types.h"
+
+int PyObjectToUniqueID(PyObject *object, object_id *objectid) {
+  if (PyObject_IsInstance(object, (PyObject *) &PyObjectIDType)) {
+    *objectid = ((PyObjectID *) object)->object_id;
+    return 1;
+  } else {
+    PyErr_SetString(PyExc_TypeError, "must be an ObjectID");
+    return 0;
+  }
+}
+
+static int PyObjectID_init(PyObjectID *self, PyObject *args, PyObject *kwds) {
+  const char *data;
+  int size;
+  if (!PyArg_ParseTuple(args, "s#", &data, &size)) {
+    return -1;
+  }
+  if (size != UNIQUE_ID_SIZE) {
+    PyErr_SetString(CommonError,
+                    "ObjectID: object id string needs to have length 20");
+    return -1;
+  }
+  memcpy(&self->object_id.id[0], data, UNIQUE_ID_SIZE);
+  return 0;
+}
+
+/* create PyObjectID from C */
+PyObject *PyObjectID_make(object_id object_id) {
+  PyObjectID *result = PyObject_New(PyObjectID, &PyObjectIDType);
+  result = (PyObjectID *) PyObject_Init((PyObject *) result, &PyObjectIDType);
+  result->object_id = object_id;
+  return (PyObject *) result;
+}
+
+static PyObject *PyObjectID_id(PyObject *self) {
+  PyObjectID *s = (PyObjectID *) self;
+  return PyString_FromStringAndSize((char *) &s->object_id.id[0],
+                                    UNIQUE_ID_SIZE);
+}
+
+static PyMethodDef PyObjectID_methods[] = {
+    {"id", (PyCFunction) PyObjectID_id, METH_NOARGS,
+     "Return the hash associated with this ObjectID"},
+    {NULL} /* Sentinel */
+};
+
+static PyMemberDef PyObjectID_members[] = {
+    {NULL} /* Sentinel */
+};
+
+PyTypeObject PyObjectIDType = {
+    PyObject_HEAD_INIT(NULL) 0, /* ob_size */
+    "common.ObjectID",          /* tp_name */
+    sizeof(PyObjectID),         /* tp_basicsize */
+    0,                          /* tp_itemsize */
+    0,                          /* tp_dealloc */
+    0,                          /* tp_print */
+    0,                          /* tp_getattr */
+    0,                          /* tp_setattr */
+    0,                          /* tp_compare */
+    0,                          /* tp_repr */
+    0,                          /* tp_as_number */
+    0,                          /* tp_as_sequence */
+    0,                          /* tp_as_mapping */
+    0,                          /* tp_hash */
+    0,                          /* tp_call */
+    0,                          /* tp_str */
+    0,                          /* tp_getattro */
+    0,                          /* tp_setattro */
+    0,                          /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT,         /* tp_flags */
+    "ObjectID object",          /* tp_doc */
+    0,                          /* tp_traverse */
+    0,                          /* tp_clear */
+    0,                          /* tp_richcompare */
+    0,                          /* tp_weaklistoffset */
+    0,                          /* tp_iter */
+    0,                          /* tp_iternext */
+    PyObjectID_methods,         /* tp_methods */
+    PyObjectID_members,         /* tp_members */
+    0,                          /* tp_getset */
+    0,                          /* tp_base */
+    0,                          /* tp_dict */
+    0,                          /* tp_descr_get */
+    0,                          /* tp_descr_set */
+    0,                          /* tp_dictoffset */
+    (initproc) PyObjectID_init, /* tp_init */
+    0,                          /* tp_alloc */
+    PyType_GenericNew,          /* tp_new */
+};
diff --git a/lib/python/serialization.c b/lib/python/serialization.c
new file mode 100644
index 000000000..82cf6417c
--- /dev/null
+++ b/lib/python/serialization.c
@@ -0,0 +1,80 @@
+#include "types.h"
+
+/* TODO(pcm): Add limit on total number of elements. */
+
+#define SIZE_LIMIT 100
+#define NUM_ELEMENTS_LIMIT 1000
+
+/**
+ * This method checks if a Python object is sufficiently simple that it can be
+ * serialized and passed by value as an argument to a task (without being put in
+ * the object store). The details of which objects are sufficiently simple are
+ * defined by this method and are not particularly important. But for
+ * performance reasons, it is better to place "small" objects in the task itself
+ * and "large" objects in the object store.
+ *
+ * @param value The Python object in question.
+ * @param num_elements_contained If this method returns 1, then the number of
+ *        objects recursively contained within this object will be added to the
+ *        value at this address. This is used to make sure that we do not
+ *        serialize objects that are too large.
+ * @return 0 if the object cannot be serialized in the task and 1 if it can.
+ */
+int is_simple_value(PyObject *value, int *num_elements_contained) {
+  *num_elements_contained += 1;
+  if (*num_elements_contained >= NUM_ELEMENTS_LIMIT) {
+    return 0;
+  }
+  if (PyInt_Check(value) || PyLong_Check(value) || value == Py_False ||
+      value == Py_True || PyFloat_Check(value) || value == Py_None) {
+    return 1;
+  }
+  if (PyString_CheckExact(value)) {
+    *num_elements_contained += PyString_Size(value);
+    return (*num_elements_contained < NUM_ELEMENTS_LIMIT);
+  }
+  if (PyUnicode_CheckExact(value)) {
+    *num_elements_contained += PyUnicode_GET_SIZE(value);
+    return (*num_elements_contained < NUM_ELEMENTS_LIMIT);
+  }
+  if (PyList_CheckExact(value) && PyList_Size(value) < SIZE_LIMIT) {
+    for (size_t i = 0; i < PyList_Size(value); ++i) {
+      if (!is_simple_value(PyList_GetItem(value, i), num_elements_contained)) {
+        return 0;
+      }
+    }
+    return (*num_elements_contained < NUM_ELEMENTS_LIMIT);
+  }
+  if (PyDict_CheckExact(value) && PyDict_Size(value) < SIZE_LIMIT) {
+    PyObject *key, *val;
+    Py_ssize_t pos = 0;
+    while (PyDict_Next(value, &pos, &key, &val)) {
+      if (!is_simple_value(key, num_elements_contained) ||
+          !is_simple_value(val, num_elements_contained)) {
+        return 0;
+      }
+    }
+    return (*num_elements_contained < NUM_ELEMENTS_LIMIT);
+  }
+  if (PyTuple_CheckExact(value) && PyTuple_Size(value) < SIZE_LIMIT) {
+    for (size_t i = 0; i < PyTuple_Size(value); ++i) {
+      if (!is_simple_value(PyTuple_GetItem(value, i), num_elements_contained)) {
+        return 0;
+      }
+    }
+    return (*num_elements_contained < NUM_ELEMENTS_LIMIT);
+  }
+  return 0;
+}
+
+PyObject *check_simple_value(PyObject *self, PyObject *args) {
+  PyObject *value;
+  if (!PyArg_ParseTuple(args, "O", &value)) {
+    return NULL;
+  }
+  int num_elements_contained = 0;
+  if (is_simple_value(value, &num_elements_contained)) {
+    Py_RETURN_TRUE;
+  }
+  Py_RETURN_FALSE;
+}
diff --git a/lib/python/setup.py b/lib/python/setup.py
new file mode 100644
index 000000000..38af43f34
--- /dev/null
+++ b/lib/python/setup.py
@@ -0,0 +1,12 @@
+from setuptools import setup, find_packages, Extension
+
+common_module = Extension("common",
+                          sources=["object_id.c", "serialization.c", "task.c"],
+                          include_dirs=["../../", "../../thirdparty"],
+                          extra_objects=["../../build/libcommon.a"],
+                          extra_compile_args=["--std=c99", "-Werror"])
+
+setup(name="Common",
+      version="0.1",
+      description="Common library for Ray",
+      ext_modules=[common_module])
diff --git a/lib/python/task.c b/lib/python/task.c
new file mode 100644
index 000000000..ef685b493
--- /dev/null
+++ b/lib/python/task.c
@@ -0,0 +1,177 @@
+#include <Python.h>
+#include "node.h"
+
+#include "types.h"
+#include "task.h"
+#include "utarray.h"
+#include "utstring.h"
+
+PyObject *CommonError;
+
+#define MARSHAL_VERSION 2
+
+static int PyTask_init(PyTask *self, PyObject *args, PyObject *kwds) {
+  function_id function_id;
+  /* Arguments of the task (can be PyObjectIDs or Python values). */
+  PyObject *arguments;
+  /* Array of pointers to string representations of pass-by-value args. */
+  UT_array *val_repr_ptrs;
+  utarray_new(val_repr_ptrs, &ut_ptr_icd);
+  int num_returns;
+  if (!PyArg_ParseTuple(args, "O&Oi", &PyObjectToUniqueID, &function_id,
+                        &arguments, &num_returns)) {
+    return -1;
+  }
+  size_t size = PyList_Size(arguments);
+  /* Determine the size of pass by value data in bytes. */
+  size_t value_data_bytes = 0;
+  for (size_t i = 0; i < size; ++i) {
+    PyObject *arg = PyList_GetItem(arguments, i);
+    if (!PyObject_IsInstance(arg, (PyObject *) &PyObjectIDType)) {
+      PyObject *data = PyMarshal_WriteObjectToString(arg, MARSHAL_VERSION);
+      value_data_bytes += PyString_Size(data);
+      utarray_push_back(val_repr_ptrs, &data);
+    }
+  }
+  /* Construct the task specification. */
+  int val_repr_index = 0;
+  self->spec =
+      alloc_task_spec(function_id, size, num_returns, value_data_bytes);
+  for (size_t i = 0; i < size; ++i) {
+    PyObject *arg = PyList_GetItem(arguments, i);
+    if (PyObject_IsInstance(arg, (PyObject *) &PyObjectIDType)) {
+      task_args_add_ref(self->spec, ((PyObjectID *) arg)->object_id);
+    } else {
+      PyObject *data =
+          *((PyObject **) utarray_eltptr(val_repr_ptrs, val_repr_index));
+      task_args_add_val(self->spec, (uint8_t *) PyString_AS_STRING(data),
+                        PyString_GET_SIZE(data));
+      Py_DECREF(data);
+      val_repr_index += 1;
+    }
+  }
+  utarray_free(val_repr_ptrs);
+  return 0;
+}
+
+static void PyTask_dealloc(PyTask *self) {
+  free_task_spec(self->spec);
+  Py_TYPE(self)->tp_free((PyObject *) self);
+}
+
+static PyObject *PyTask_function_id(PyObject *self) {
+  function_id function_id = *task_function(((PyTask *) self)->spec);
+  return PyObjectID_make(function_id);
+}
+
+static PyObject *PyTask_arguments(PyObject *self, PyObject *args) {
+  int arg_index;
+  task_spec *spec = ((PyTask *) self)->spec;
+  if (!PyArg_ParseTuple(args, "i", &arg_index)) {
+    return NULL;
+  }
+  if (task_arg_type(spec, arg_index) == ARG_BY_REF) {
+    object_id object_id = *task_arg_id(spec, arg_index);
+    return PyObjectID_make(object_id);
+  } else {
+    PyObject *s = PyMarshal_ReadObjectFromString(
+        (char *) task_arg_val(spec, arg_index),
+        (Py_ssize_t) task_arg_length(spec, arg_index));
+    Py_DECREF(s);
+    Py_RETURN_NONE;
+  }
+}
+
+static PyObject *PyTask_returns(PyObject *self, PyObject *args) {
+  int ret_index;
+  if (!PyArg_ParseTuple(args, "i", &ret_index)) {
+    return NULL;
+  }
+  object_id object_id = *task_return(((PyTask *) self)->spec, ret_index);
+  return PyObjectID_make(object_id);
+}
+
+static PyMethodDef PyTask_methods[] = {
+    {"function_id", (PyCFunction) PyTask_function_id, METH_NOARGS,
+     "Return the function id associated with this task."},
+    {"arguments", (PyCFunction) PyTask_arguments, METH_VARARGS,
+     "Return the i-th argument of the task."},
+    {"returns", (PyCFunction) PyTask_returns, METH_VARARGS,
+     "Return the i-th object reference of the task."},
+    {NULL} /* Sentinel */
+};
+
+static PyTypeObject PyTaskType = {
+    PyObject_HEAD_INIT(NULL) 0,  /* ob_size */
+    "task.Task",                 /* tp_name */
+    sizeof(PyTask),              /* tp_basicsize */
+    0,                           /* tp_itemsize */
+    (destructor) PyTask_dealloc, /* tp_dealloc */
+    0,                           /* tp_print */
+    0,                           /* tp_getattr */
+    0,                           /* tp_setattr */
+    0,                           /* tp_compare */
+    0,                           /* tp_repr */
+    0,                           /* tp_as_number */
+    0,                           /* tp_as_sequence */
+    0,                           /* tp_as_mapping */
+    0,                           /* tp_hash */
+    0,                           /* tp_call */
+    0,                           /* tp_str */
+    0,                           /* tp_getattro */
+    0,                           /* tp_setattro */
+    0,                           /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT,          /* tp_flags */
+    "Task object",               /* tp_doc */
+    0,                           /* tp_traverse */
+    0,                           /* tp_clear */
+    0,                           /* tp_richcompare */
+    0,                           /* tp_weaklistoffset */
+    0,                           /* tp_iter */
+    0,                           /* tp_iternext */
+    PyTask_methods,              /* tp_methods */
+    0,                           /* tp_members */
+    0,                           /* tp_getset */
+    0,                           /* tp_base */
+    0,                           /* tp_dict */
+    0,                           /* tp_descr_get */
+    0,                           /* tp_descr_set */
+    0,                           /* tp_dictoffset */
+    (initproc) PyTask_init,      /* tp_init */
+    0,                           /* tp_alloc */
+    PyType_GenericNew,           /* tp_new */
+};
+
+static PyMethodDef common_methods[] = {
+    {"check_simple_value", check_simple_value, METH_VARARGS,
+     "Should the object be passed by value?"},
+    {NULL} /* Sentinel */
+};
+
+#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */
+#define PyMODINIT_FUNC void
+#endif
+
+PyMODINIT_FUNC initcommon(void) {
+  PyObject *m;
+
+  if (PyType_Ready(&PyTaskType) < 0)
+    return;
+
+  if (PyType_Ready(&PyObjectIDType) < 0)
+    return;
+
+  m = Py_InitModule3("common", common_methods,
+                     "Example module that creates an extension type.");
+
+  Py_INCREF(&PyTaskType);
+  PyModule_AddObject(m, "Task", (PyObject *) &PyTaskType);
+
+  Py_INCREF(&PyObjectIDType);
+  PyModule_AddObject(m, "ObjectID", (PyObject *) &PyObjectIDType);
+
+  char common_error[] = "common.error";
+  CommonError = PyErr_NewException(common_error, NULL, NULL);
+  Py_INCREF(CommonError);
+  PyModule_AddObject(m, "common_error", CommonError);
+}
diff --git a/lib/python/types.h b/lib/python/types.h
new file mode 100644
index 000000000..9e30581b5
--- /dev/null
+++ b/lib/python/types.h
@@ -0,0 +1,33 @@
+#ifndef TYPES_H
+#define TYPES_H
+
+#include <Python.h>
+#include "marshal.h"
+#include "structmember.h"
+
+#include "common.h"
+#include "task.h"
+
+extern PyObject *CommonError;
+
+// clang-format off
+typedef struct {
+  PyObject_HEAD
+  object_id object_id;
+} PyObjectID;
+
+typedef struct {
+  PyObject_HEAD
+  task_spec *spec;
+} PyTask;
+// clang-format on
+
+extern PyTypeObject PyObjectIDType;
+
+int PyObjectToUniqueID(PyObject *object, object_id *objectid);
+
+PyObject *PyObjectID_make(object_id object_id);
+
+PyObject *check_simple_value(PyObject *self, PyObject *args);
+
+#endif /* TYPES_H */
diff --git a/task.h b/task.h
index 9267edb65..28886bf14 100644
--- a/task.h
+++ b/task.h
@@ -13,7 +13,6 @@
 #include "utstring.h"
 
 typedef unique_id function_id;
-typedef unique_id object_id;
 
 /* The task ID is a deterministic hash of the function ID that
  * the task executes and the argument IDs or argument values */
diff --git a/test/test.py b/test/test.py
new file mode 100644
index 000000000..bbed21376
--- /dev/null
+++ b/test/test.py
@@ -0,0 +1,51 @@
+from __future__ import print_function
+
+import unittest
+
+import common
+
+BASE_SIMPLE_OBJECTS = [
+  0, 1, 100000, 0L, 1L, 100000L, 1L << 100, 0.0, 0.5, 0.9, 100000.1, (), [], {},
+  "", 990 * "h", u"", 990 * u"h"
+]
+
+LIST_SIMPLE_OBJECTS = [[obj] for obj in BASE_SIMPLE_OBJECTS]
+TUPLE_SIMPLE_OBJECTS = [(obj,) for obj in BASE_SIMPLE_OBJECTS]
+DICT_SIMPLE_OBJECTS = [{(): obj} for obj in BASE_SIMPLE_OBJECTS]
+
+SIMPLE_OBJECTS = (BASE_SIMPLE_OBJECTS +
+                  LIST_SIMPLE_OBJECTS +
+                  TUPLE_SIMPLE_OBJECTS +
+                  DICT_SIMPLE_OBJECTS)
+
+# Create some complex objects that cannot be serialized by value in tasks.
+
+l = []
+l.append(l)
+
+class Foo(object):
+  def __init__(self):
+    pass
+
+BASE_COMPLEX_OBJECTS = [999 * "h", 999 * u"h", l, Foo(), 10 * [10 * [10 * [1]]]]
+
+LIST_COMPLEX_OBJECTS = [[obj] for obj in BASE_COMPLEX_OBJECTS]
+TUPLE_COMPLEX_OBJECTS = [(obj,) for obj in BASE_COMPLEX_OBJECTS]
+DICT_COMPLEX_OBJECTS = [{(): obj} for obj in BASE_COMPLEX_OBJECTS]
+
+COMPLEX_OBJECTS = (BASE_COMPLEX_OBJECTS +
+                   LIST_COMPLEX_OBJECTS +
+                   TUPLE_COMPLEX_OBJECTS +
+                   DICT_COMPLEX_OBJECTS)
+
+class TestPlasmaClient(unittest.TestCase):
+
+  def test_serialize_by_value(self):
+
+    for val in SIMPLE_OBJECTS:
+      self.assertTrue(common.check_simple_value(val))
+    for val in COMPLEX_OBJECTS:
+      self.assertFalse(common.check_simple_value(val))
+
+if __name__ == "__main__":
+  unittest.main(verbosity=2)