diff --git a/os_traits/__init__.py b/os_traits/__init__.py
index 8b6a3d2..109423c 100644
--- a/os_traits/__init__.py
+++ b/os_traits/__init__.py
@@ -74,3 +74,12 @@ def check_traits(traits):
     valid_traits = trait_set & valid_trait_set
 
     return (valid_traits, trait_set - valid_traits)
+
+
+def is_custom(trait):
+    """Returns True if the trait string represents a custom trait, or False
+    otherwise.
+
+    :param trait: String name of the trait
+    """
+    return trait.startswith(NAMESPACES['CUSTOM'])
diff --git a/os_traits/const.py b/os_traits/const.py
index 81d068a..e576971 100644
--- a/os_traits/const.py
+++ b/os_traits/const.py
@@ -12,6 +12,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+# Any user-specified feature/trait is prefixed with the custom namespace
+_CUSTOM_NS = 'CUSTOM_'
+
 # All hardware-specific features are prefixed with this namespace
 _HW_NS = 'HW_'
 
@@ -68,6 +71,7 @@ HW_CPU_X86_VMX = _CPU_X86_NS + 'VMX'
 HW_CPU_X86_SVM = _CPU_X86_NS + 'SVM'
 
 NAMESPACES = {
+    'CUSTOM': _CUSTOM_NS,
     'HARDWARE': _HW_NS,
     'HW': _HW_NS,
     'CPU': _CPU_NS,
diff --git a/os_traits/tests/test_os_traits.py b/os_traits/tests/test_os_traits.py
index 0d5e011..fa490d5 100644
--- a/os_traits/tests/test_os_traits.py
+++ b/os_traits/tests/test_os_traits.py
@@ -37,7 +37,7 @@ class TestOs_traits(base.TestCase):
     def test_namespaces(self):
         namespaces = ot.NAMESPACES
         self.assertIn(("HARDWARE", "HW_"), namespaces.items())
-        self.assertEqual(4, len(namespaces))
+        self.assertEqual(5, len(namespaces))
 
     def test_get_traits(self):
         traits = ot.get_traits(ot.NAMESPACES['X86'])
@@ -53,3 +53,7 @@ class TestOs_traits(base.TestCase):
         check_traits.extend(not_traits)
         self.assertEqual((traits, not_traits),
                          ot.check_traits(check_traits))
+
+    def test_is_custom(self):
+        self.assertTrue(ot.is_custom('CUSTOM_FOO'))
+        self.assertFalse(ot.is_custom('HW_CPU_X86_SSE42'))