diff --git a/wagtail/images/fields.py b/wagtail/images/fields.py
index e9492567f..2c4919ea1 100644
--- a/wagtail/images/fields.py
+++ b/wagtail/images/fields.py
@@ -7,8 +7,8 @@ from django.forms.fields import ImageField
 from django.template.defaultfilters import filesizeformat
 from django.utils.translation import ugettext_lazy as _
 
-ALLOWED_EXTENSIONS = ['gif', 'jpg', 'jpeg', 'png']
-SUPPORTED_FORMATS_TEXT = _("GIF, JPEG, PNG")
+ALLOWED_EXTENSIONS = ['gif', 'jpg', 'jpeg', 'png', 'webp']
+SUPPORTED_FORMATS_TEXT = _("GIF, JPEG, PNG, WEBP")
 
 
 class WagtailImageField(ImageField):
diff --git a/wagtail/images/models.py b/wagtail/images/models.py
index e07973005..424786e21 100644
--- a/wagtail/images/models.py
+++ b/wagtail/images/models.py
@@ -297,6 +297,7 @@ class AbstractImage(CollectionMember, index.Indexed, models.Model):
                 'jpeg': '.jpg',
                 'png': '.png',
                 'gif': '.gif',
+                'webp': '.webp',
             }
 
             output_extension = filter.spec.replace('|', '.') + FORMAT_EXTENSIONS[generated_image.format_name]
@@ -414,6 +415,10 @@ class Filter:
                 if original_format == 'gif' and not willow.has_animation():
                     output_format = 'png'
 
+                # Convert WEBP files to PNG
+                if original_format == 'webp':
+                    output_format = 'png'
+
             if output_format == 'jpeg':
                 # Allow changing of JPEG compression quality
                 if 'jpeg-quality' in env:
@@ -432,6 +437,8 @@ class Filter:
                 return willow.save_as_png(output, optimize=True)
             elif output_format == 'gif':
                 return willow.save_as_gif(output)
+            elif output_format == 'webp':
+                return willow.save_as_webp(output)
 
     def get_cache_key(self, image):
         vary_parts = []
diff --git a/wagtail/images/tests/test_admin_views.py b/wagtail/images/tests/test_admin_views.py
index 1248339c0..e7d088a23 100644
--- a/wagtail/images/tests/test_admin_views.py
+++ b/wagtail/images/tests/test_admin_views.py
@@ -853,7 +853,7 @@ class TestImageChooserUploadView(TestCase, WagtailTestUtils):
 
         self.assertEqual(response.status_code, 200)
         self.assertTemplateUsed(response, 'wagtailimages/chooser/chooser.html')
-        self.assertFormError(response, 'uploadform', 'file', "Not a supported image format. Supported formats: GIF, JPEG, PNG.")
+        self.assertFormError(response, 'uploadform', 'file', "Not a supported image format. Supported formats: GIF, JPEG, PNG, WEBP.")
 
         # the action URL of the re-rendered form should include the select_format=true parameter
         # (NB the HTML in the response is embedded in a JS string, so need to escape accordingly)
@@ -1050,7 +1050,7 @@ class TestMultipleImageUploader(TestCase, WagtailTestUtils):
         self.assertIn('error_message', response_json)
         self.assertFalse(response_json['success'])
         self.assertEqual(
-            response_json['error_message'], "Not a supported image format. Supported formats: GIF, JPEG, PNG."
+            response_json['error_message'], "Not a supported image format. Supported formats: GIF, JPEG, PNG, WEBP."
         )
 
     def test_edit_get(self):