diff --git a/docsite/rst/playbooks_variables.rst b/docsite/rst/playbooks_variables.rst
index 82d28c71eef..1e61cecbb01 100644
--- a/docsite/rst/playbooks_variables.rst
+++ b/docsite/rst/playbooks_variables.rst
@@ -180,6 +180,27 @@ Jinja2 provides a useful 'default' filter, that is often a better approach to fa
 In the above example, if the variable 'some_variable' is not defined, the value used will be 5, rather than an error
 being raised.
 
+
+.. _omitting_undefined_variables:
+
+Omitting Undefined Variables and Parameters
+-------------------------------------------
+
+As of Ansible 1.8, it is possible to use the default filter to omit variables and module parameters using the special
+`omit` variable::
+
+    - name: touch files with an optional mode
+      file: dest={{item.path}} state=touch mode={{item.mode|default(omit)}}
+      with_items:
+        - path: /tmp/foo
+        - path: /tmp/bar
+        - path: /tmp/baz
+          mode: "0444"
+
+For the first two files in the list, the default mode will be determined by the umask of the system as the `mode=`
+parameter will not be sent to the file module while the final file will receive the `mode=0444` option.
+
+
 .. _list_filters:
 
 List Filters
diff --git a/lib/ansible/runner/__init__.py b/lib/ansible/runner/__init__.py
index a63bf426533..b7bfc7bd3c0 100644
--- a/lib/ansible/runner/__init__.py
+++ b/lib/ansible/runner/__init__.py
@@ -46,12 +46,17 @@ import connection
 from return_data import ReturnData
 from ansible.callbacks import DefaultRunnerCallbacks, vv
 from ansible.module_common import ModuleReplacer
-from ansible.module_utils.splitter import split_args
+from ansible.module_utils.splitter import split_args, unquote
 from ansible.cache import FactCache
 from ansible.utils import update_hash
 
 module_replacer = ModuleReplacer(strip_comments=False)
 
+try:
+    from hashlib import md5 as _md5
+except ImportError:
+    from md5 import md5 as _md5
+
 HAS_ATFORK=True
 try:
     from Crypto.Random import atfork
@@ -202,6 +207,7 @@ class Runner(object):
         self.su_user_var      = su_user
         self.su_user          = None
         self.su_pass          = su_pass
+        self.omit_token       = '__omit_place_holder__%s' % _md5(os.urandom(64)).hexdigest()
         self.vault_pass       = vault_pass
         self.no_log           = no_log
         self.run_once         = run_once
@@ -623,6 +629,7 @@ class Runner(object):
         inject['defaults']    = self.default_vars
         inject['environment'] = self.environment
         inject['playbook_dir'] = os.path.abspath(self.basedir)
+        inject['omit']        = self.omit_token
 
         # template this one is available, callbacks use this
         delegate_to = self.module_vars.get('delegate_to')
@@ -740,14 +747,6 @@ class Runner(object):
         if self.su_user_var is not None:
             self.su_user = template.template(self.basedir, self.su_user_var, inject)
 
-        # allow module args to work as a dictionary
-        # though it is usually a string
-        new_args = ""
-        if type(module_args) == dict:
-            for (k,v) in module_args.iteritems():
-                new_args = new_args + "%s='%s' " % (k,v)
-            module_args = new_args
-
         # module_name may be dynamic (but cannot contain {{ ansible_ssh_user }})
         module_name  = template.template(self.basedir, module_name, inject)
 
@@ -872,6 +871,11 @@ class Runner(object):
         if self._early_needs_tmp_path(module_name, handler):
             tmp = self._make_tmp_path(conn)
 
+        # allow module args to work as a dictionary
+        # though it is usually a string
+        if isinstance(module_args, dict):
+            module_args = utils.serialize_args(module_args)
+
         # render module_args and complex_args templates
         try:
             # When templating module_args, we need to be careful to ensure
@@ -892,6 +896,24 @@ class Runner(object):
         except jinja2.exceptions.UndefinedError, e:
             raise errors.AnsibleUndefinedVariable("One or more undefined variables: %s" % str(e))
 
+        # filter omitted arguments out from complex_args
+        if complex_args:
+            complex_args = dict(filter(lambda x: x[1] != self.omit_token, complex_args.iteritems()))
+
+        # Filter omitted arguments out from module_args.
+        # We do this with split_args instead of parse_kv to ensure
+        # that things are not unquoted/requoted incorrectly
+        args = split_args(module_args)
+        final_args = []
+        for arg in args:
+            if '=' in arg:
+                k,v = arg.split('=', 1)
+                if unquote(v) != self.omit_token:
+                    final_args.append(arg)
+            else:
+                # not a k=v param, append it
+                final_args.append(arg)
+        module_args = ' '.join(final_args)
 
         result = handler.run(conn, tmp, module_name, module_args, inject, complex_args)
         # Code for do until feature
diff --git a/lib/ansible/runner/filter_plugins/core.py b/lib/ansible/runner/filter_plugins/core.py
index 7ca0f937420..61b80bce2c5 100644
--- a/lib/ansible/runner/filter_plugins/core.py
+++ b/lib/ansible/runner/filter_plugins/core.py
@@ -31,6 +31,7 @@ from distutils.version import LooseVersion, StrictVersion
 from random import SystemRandom
 from jinja2.filters import environmentfilter
 
+
 def to_nice_yaml(*a, **kw):
     '''Make verbose, human readable yaml'''
     return yaml.safe_dump(*a, indent=4, allow_unicode=True, default_flow_style=False, **kw)
@@ -234,6 +235,7 @@ def rand(environment, end, start=None, step=None):
     else:
         raise errors.AnsibleFilterError('random can only be used on sequences and integers')
 
+
 class FilterModule(object):
     ''' Ansible core jinja2 filters '''
 
@@ -306,4 +308,3 @@ class FilterModule(object):
             # random numbers
             'random': rand,
         }
-
diff --git a/lib/ansible/utils/__init__.py b/lib/ansible/utils/__init__.py
index 131a3e315df..aa0a1b8ee71 100644
--- a/lib/ansible/utils/__init__.py
+++ b/lib/ansible/utils/__init__.py
@@ -61,6 +61,7 @@ LOOKUP_REGEX = re.compile(r'lookup\s*\(')
 PRINT_CODE_REGEX = re.compile(r'(?:{[{%]|[%}]})')
 CODE_REGEX = re.compile(r'(?:{%|%})')
 
+
 try:
     import json
 except ImportError:
@@ -110,6 +111,7 @@ try:
 except ImportError:
     pass
 
+
 ###############################################################
 # Abstractions around keyczar
 ###############################################################
@@ -543,6 +545,18 @@ def parse_json(raw_data, from_remote=False, from_inventory=False):
 
     return results
 
+def serialize_args(args):
+    '''
+    Flattens a dictionary args to a k=v string
+    '''
+    module_args = ""
+    for (k,v) in args.iteritems():
+        if isinstance(v, basestring):
+            module_args = "%s=%s %s" % (k, pipes.quote(v), module_args)
+        elif isinstance(v, bool):
+            module_args = "%s=%s %s" % (k, str(v), module_args)
+    return module_args.strip()
+
 def merge_module_args(current_args, new_args):
     '''
     merges either a dictionary or string of k=v pairs with another string of k=v pairs,
@@ -557,14 +571,7 @@ def merge_module_args(current_args, new_args):
     elif isinstance(new_args, basestring):
         new_args_kv = parse_kv(new_args)
         final_args.update(new_args_kv)
-    # then we re-assemble into a string
-    module_args = ""
-    for (k,v) in final_args.iteritems():
-        if isinstance(v, basestring):
-            module_args = "%s=%s %s" % (k, pipes.quote(v), module_args)
-        elif isinstance(v, bool):
-            module_args = "%s=%s %s" % (k, str(v), module_args)
-    return module_args.strip()
+    return serialize_args(final_args)
 
 def parse_yaml(data, path_hint=None):
     ''' convert a yaml string to a data structure.  Also supports JSON, ssssssh!!!'''
diff --git a/test/integration/roles/test_good_parsing/tasks/main.yml b/test/integration/roles/test_good_parsing/tasks/main.yml
index 6461d8e7728..27475ce0f53 100644
--- a/test/integration/roles/test_good_parsing/tasks/main.yml
+++ b/test/integration/roles/test_good_parsing/tasks/main.yml
@@ -172,3 +172,33 @@
   assert:
     that:
       - nested_include_var is undefined
+
+- name: test omit in complex args
+  set_fact:
+    foo: bar
+    spam: "{{ omit }}"
+    should_not_omit: "prefix{{ omit }}"
+
+- assert:
+    that:
+      - foo == 'bar'
+      - spam is undefined
+      - should_not_omit is defined
+
+- name: test omit in module args
+  set_fact: >
+    yo=whatsup
+    eggs="{{ omit }}"
+    default_omitted="{{ not_exists|default(omit) }}"
+    should_not_omit_1="prefix{{ omit }}"
+    should_not_omit_2="{{ omit }}suffix"
+    should_not_omit_3="__omit_place_holder__afb6b9bc3d20bfeaa00a1b23a5930f89"
+
+- assert:
+    that:
+      - yo == 'whatsup'
+      - eggs is undefined
+      - default_omitted is undefined
+      - should_not_omit_1 is defined
+      - should_not_omit_2 is defined
+      - should_not_omit_3 == "__omit_place_holder__afb6b9bc3d20bfeaa00a1b23a5930f89"