diff --git a/configspec/manager.py b/configspec/manager.py
index ef095eb..9e20f7d 100644
--- a/configspec/manager.py
+++ b/configspec/manager.py
@@ -186,7 +186,7 @@ class ConfigManager():
         self.root_config[bundle_name] = bundle_source
         return deepcopy(bundle_source)
 
-    def validate_bundles(self, bundle_names):
+    def validate_bundles(self, bundle_names=None):
         """
         Validate multiple config bundles at once, validating each one with the corresponding
         ConfigSpecification stored in the ConfigManager. See ``validate_bundle()``.
@@ -200,6 +200,8 @@ class ConfigManager():
             dict: A dict of deepcopied config bundles, with keys matching those passed in
                 ``bundle_names``.
         """
+        if bundle_names is None:
+            bundle_names = self.get_bundle_names()
 
         config_values = {}
         if isinstance(bundle_names, dict):
@@ -233,7 +235,7 @@ class ConfigManager():
 
         return self.root_config[bundle_name]
 
-    def get_config_bundles(self, bundle_names):
+    def get_config_bundles(self, bundle_names=None):
         """
         Get multiple config bundles at once. If not yet validated, each will validate
         their config source against the corresponding config specification stored in the
@@ -246,6 +248,8 @@ class ConfigManager():
             dict: A dict of validated config bundles, with keys matching those passed in
                 ``bundle_names``.
         """
+        if bundle_names is None:
+            bundle_names = self.get_bundle_names()
 
         config_values = {}
         if isinstance(bundle_names, str):