diff --git a/objpool/__init__.py b/objpool/__init__.py
index d1c18e3..1316dbe 100644
--- a/objpool/__init__.py
+++ b/objpool/__init__.py
@@ -57,6 +57,16 @@
 log = logging.getLogger(__name__)
 
 
+class DummySemaphore(object):
+    _Semaphore__value = 0
+
+    def acquire(self, *args, **kwargs):
+        return True
+
+    def release(self):
+        pass
+
+
 class ObjectPoolError(Exception):
     pass
 
@@ -114,16 +124,28 @@ class ObjectPool(object):
       relies upon will be copied when the new process is being created.
 
     """
-    def __init__(self, size=None):
+    def __init__(self, size=None, create=None, verify=None, cleanup=None):
         self._pool_pid = getpid()
+        if size is None:
+            size = 0
+
         try:
-            self.size = int(size)
-            assert size >= 1
+            int(size)
+            assert size >= 0
         except:
-            raise ValueError("Invalid size for pool (positive integer "
+            raise ValueError("Invalid size for pool (non-negative integer "
                              "required): %r" % (size,))
 
-        self._semaphore = Semaphore(size)  # Pool grows up to size limit
+        self._create_func = create
+        self._verify_func = verify
+        self._cleanup_func = cleanup
+
+        self.size = size
+        if self.size > 0:
+            self._semaphore = Semaphore(self.size)
+        else:
+            self._semaphore = DummySemaphore()
+
         self._mutex = Lock()  # Protect shared _set oject
         self._set = set()
         log.debug("Initialized pool %r", self)
@@ -237,7 +259,9 @@ def _pool_create(self):
         Must be thread-safe.
 
         """
-        raise NotImplementedError
+        if self._create_func is None:
+            raise NotImplementedError
+        return self._create_func()
 
     def _pool_verify(self, obj):
         """Verify an object after getting it from the pool.
@@ -249,7 +273,9 @@ def _pool_verify(self, obj):
         Must be thread-safe.
 
         """
-        raise NotImplementedError
+        if self._verify_func is None:
+            return True
+        return self._verify_func(obj)
 
     def _pool_cleanup(self, obj):
         """Cleanup an object before being put back into the pool.
@@ -259,7 +285,8 @@ def _pool_cleanup(self, obj):
         Must be thread-safe.
 
         """
-        raise NotImplementedError
+        if self._cleanup_func is not None:
+            return self._cleanup_func(obj)
 
 
 class PooledObject(object):
diff --git a/objpool/test/tests.py b/objpool/test/tests.py
index 86fe745..6893c63 100644
--- a/objpool/test/tests.py
+++ b/objpool/test/tests.py
@@ -107,12 +107,20 @@ def _pool_cleanup(self, obj):
 
 
 class ObjectPoolTestCase(unittest.TestCase):
-    def test_create_pool_requires_size(self):
+    def test_create_pool_invalid_sizes(self):
         """Test __init__() requires valid size argument"""
-        self.assertRaises(ValueError, ObjectPool)
-        self.assertRaises(ValueError, ObjectPool, size="size10")
-        self.assertRaises(ValueError, ObjectPool, size=0)
         self.assertRaises(ValueError, ObjectPool, size=-1)
+        self.assertRaises(ValueError, ObjectPool, size="size10")
+
+    def test_create_pool_valid_sizes(self):
+        ObjectPool(size=0)
+        ObjectPool(size=None)
+
+    def test_unbounded_pool(self):
+        pool = ObjectPool(size=0, create=[1,2,3].pop)
+        self.assertEqual(pool.pool_get(), 3)
+        self.assertEqual(pool.pool_get(), 2)
+        self.assertEqual(pool.pool_get(), 1)
 
     def test_create_pool(self):
         """Test pool creation works"""
@@ -123,12 +131,27 @@ def test_get_not_implemented(self):
         """Test pool_get() method not implemented in abstract class"""
         pool = ObjectPool(100)
         self.assertRaises(NotImplementedError, pool._pool_create)
-        self.assertRaises(NotImplementedError, pool._pool_verify, None)
 
-    def test_put_not_implemented(self):
-        """Test pool_put() method not implemented in abstract class"""
-        pool = ObjectPool(100)
-        self.assertRaises(NotImplementedError, pool._pool_cleanup, None)
+    def test_get_with_factory(self):
+        obj_generator = iter(range(10)).next
+        pool = ObjectPool(3, create=obj_generator)
+        self.assertEqual(pool.pool_get(), 0)
+        self.assertEqual(pool.pool_get(), 1)
+        self.assertEqual(pool.pool_get(), 2)
+
+    def test_put_with_factory(self):
+        cleaned_objects = []
+        pool = ObjectPool(3,
+            create=[2, 1, 0].pop,
+            verify=lambda o: o % 2 == 0,
+            cleanup=cleaned_objects.append,
+        )
+        self.assertEqual(pool.pool_get(), 0)
+        pool.pool_put(0)
+        self.assertEqual(pool.pool_get(), 0)
+        self.assertRaises(PoolVerificationError, pool.pool_get)
+        self.assertEqual(pool.pool_get(), 2)
+        self.assertEqual(cleaned_objects, [0])
 
 
 class NumbersPoolTestCase(unittest.TestCase):