diff --git a/testing/taskcluster/docs/index.rst b/testing/taskcluster/docs/index.rst
index 0611baeb2aa3..a9b8c50c18f0 100644
--- a/testing/taskcluster/docs/index.rst
+++ b/testing/taskcluster/docs/index.rst
@@ -171,6 +171,31 @@ additional-parameters
    *optional* Dictionary of additional parameters to pass to template
    expansion.
 
+when
+   *optional* Dictionary of conditions that must be met for this task
+   to run. See the section below for more details.
+
+Conditional Execution
+---------------------
+
+The ``when`` generic task dictionary entry can declare conditions that
+must be true for a task to run. Valid entries in this dictionary are
+described below.
+
+file_patterns
+   List of path patterns that will be matched against all files changed.
+
+   The set of changed files is obtained from version control. If the changed
+   files could not be determined, this condition is ignored and no filtering
+   occurs.
+
+   Values use the ``mozpack`` matching code. ``*`` is a wildcard for
+   all path characters except ``/``. ``**`` matches all directories. To
+   e.g. match against all ``.js`` files, one would use ``**/*.js``.
+
+   If a single pattern matches a single changed file, the task will be
+   scheduled.
+
 Developing
 ==========
 
diff --git a/testing/taskcluster/mach_commands.py b/testing/taskcluster/mach_commands.py
index 64eed0366464..7033a1327af2 100644
--- a/testing/taskcluster/mach_commands.py
+++ b/testing/taskcluster/mach_commands.py
@@ -274,9 +274,14 @@ class Graph(object):
     @CommandArgument('--dry-run',
         action='store_true', default=False,
         help="Stub out taskIds and date fields from the task definitions.")
+    @CommandArgument('--ignore-conditions',
+        action='store_true',
+        help='Run tasks even if their conditions are not met')
     def create_graph(self, **params):
         from functools import partial
 
+        from mozpack.path import match as mozpackmatch
+
         from slugid import nice as slugid
 
         import taskcluster_graph.transform.routes as routes_transform
@@ -324,6 +329,7 @@ class Graph(object):
         # Default to current time if querying the head rev fails
         pushdate = time.strftime('%Y%m%d%H%M%S', time.gmtime())
         vcs_info = query_vcs_info(params['head_repository'], params['head_rev'])
+        changed_files = set()
         if vcs_info:
             pushdate = time.strftime('%Y%m%d%H%M%S', time.gmtime(vcs_info.pushdate))
 
@@ -333,6 +339,8 @@ class Graph(object):
                 sys.stderr.write('%s %s\n' % (
                     c['node'][0:12], c['desc'].splitlines()[0]))
 
+                changed_files |= set(c['files'])
+
         # Template parameters used when expanding the graph
         seen_images = {}
         parameters = dict(gaia_info().items() + {
@@ -390,6 +398,41 @@ class Graph(object):
             'name': 'task graph local'
         }
 
+        # Filter the job graph according to conditions met by this invocation run.
+        def should_run(task):
+            # Old style build or test task that doesn't define conditions. Always runs.
+            if 'when' not in task:
+                return True
+
+            # Command line override to not filter.
+            if params['ignore_conditions']:
+                return True
+
+            when = task['when']
+
+            # If the task defines file patterns and we have a set of changed
+            # files to compare against, only run if a file pattern matches one
+            # of the changed files.
+            file_patterns = when.get('file_patterns', None)
+            if file_patterns and changed_files:
+                for pattern in file_patterns:
+                    for path in changed_files:
+                        if mozpackmatch(path, pattern):
+                            sys.stderr.write('scheduling %s because pattern %s '
+                                             'matches %s\n' % (task['task'],
+                                                               pattern,
+                                                               path))
+                            return True
+
+                # No file patterns matched. Discard task.
+                sys.stderr.write('discarding %s because no relevant files changed\n' %
+                                 task['task'])
+                return False
+
+            return True
+
+        job_graph = filter(should_run, job_graph)
+
         all_routes = {}
 
         for build in job_graph:
diff --git a/testing/taskcluster/taskcluster_graph/commit_parser.py b/testing/taskcluster/taskcluster_graph/commit_parser.py
index a2f9b7a86d61..369c4cda8f1c 100644
--- a/testing/taskcluster/taskcluster_graph/commit_parser.py
+++ b/testing/taskcluster/taskcluster_graph/commit_parser.py
@@ -350,6 +350,7 @@ def parse_commit(message, jobs):
             # TODO support declaring a different build type
             'build_type': name,
             'interactive': args.interactive,
+            'when': task.get('when', {})
         })
 
     # Times that test jobs will be scheduled
diff --git a/testing/taskcluster/tasks/branches/base_jobs.yml b/testing/taskcluster/tasks/branches/base_jobs.yml
index b5adbbfd5416..835890f56cda 100644
--- a/testing/taskcluster/tasks/branches/base_jobs.yml
+++ b/testing/taskcluster/tasks/branches/base_jobs.yml
@@ -309,4 +309,19 @@ tests:
 tasks:
   eslint-gecko:
     task: tasks/tests/eslint-gecko.yml
-    root: true
\ No newline at end of file
+    root: true
+    when:
+      file_patterns:
+        # Files that are likely audited.
+        - '**/*.js'
+        - '**/*.jsm'
+        - '**/*.jsx'
+        - '**/*.html'
+        - '**/*.xml'
+        # Run when eslint policies change.
+        - '**/.eslintignore'
+        - '**/*eslintrc*'
+        # The plugin implementing custom checks.
+        - 'testing/eslint-plugin-mozilla/**'
+        # Other misc lint related files.
+        - 'tools/lint/**'