diff --git a/.github/ISSUE_TEMPLATE.md b/.github/ISSUE_TEMPLATE.md
index 8d68054f92..ffe1bc4655 100644
--- a/.github/ISSUE_TEMPLATE.md
+++ b/.github/ISSUE_TEMPLATE.md
@@ -10,7 +10,7 @@ If you are asking a question rather than filing a bug, try one of these instead:
 
 #### Live Demo
 <!-- jsBin starting point (fork and edit) -->
-https://jsbin.com/luhaxab/1/edit
+https://jsbin.com/luhaxab/edit
 <!-- glitch.me starting point (remix and edit -- must be logged in to persist!) -->
 https://glitch.com/edit/#!/polymer-repro?path=my-element.html:2:0
 <!-- ...or provide your own repro URL -->
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d2437a76b0..364ecdcd15 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,130 @@
 # Change Log
 
+## [v2.6.0](https://github.com/Polymer/polymer/tree/v2.6.0) (2018-03-22)
+- Use function instead of Set ([commit](https://github.com/Polymer/polymer/commit/33d2e1a8))
+
+- [ci skip] Fix typo ([commit](https://github.com/Polymer/polymer/commit/0d1b1c2e))
+
+- Fix test in shady DOM ([commit](https://github.com/Polymer/polymer/commit/a586b72c))
+
+- Deduplicate style includes ([commit](https://github.com/Polymer/polymer/commit/acfef71d))
+
+- use a clearer test for shadowRoot ([commit](https://github.com/Polymer/polymer/commit/b2fb1cfd))
+
+- Returning null in template should nullify parent template ([commit](https://github.com/Polymer/polymer/commit/2a6c0a2a))
+
+- [ci skip] Add clarifying comment ([commit](https://github.com/Polymer/polymer/commit/0573d483))
+
+- Correct the JSBin version ([commit](https://github.com/Polymer/polymer/commit/cb1ae7d3))
+
+- Put attribute capitalization fix in property-effects ([commit](https://github.com/Polymer/polymer/commit/d45dd575))
+
+- Add note about pre v3 releases ([commit](https://github.com/Polymer/polymer/commit/f9391618))
+
+- Add note for npm package ([commit](https://github.com/Polymer/polymer/commit/8f2cc0d5))
+
+- Add iron-component-page dev-dependency ([commit](https://github.com/Polymer/polymer/commit/d93dd1ce))
+
+- Update several gulp dependencies ([commit](https://github.com/Polymer/polymer/commit/ca57a1f3))
+
+- Update dom5 to 3.0.0 ([commit](https://github.com/Polymer/polymer/commit/d4a0914e))
+
+- Update Google Closure Compiler version and fix cast ([commit](https://github.com/Polymer/polymer/commit/4004c9c4))
+
+- Update types ([commit](https://github.com/Polymer/polymer/commit/bb61a20d))
+
+- Fix several issues in the documentation of dom-* elements ([commit](https://github.com/Polymer/polymer/commit/8e1b3f45))
+
+- Handle `disabled` attribute correctly for tap gesture ([commit](https://github.com/Polymer/polymer/commit/5c0f3e6a))
+
+- add test case for nested label ([commit](https://github.com/Polymer/polymer/commit/c11c99b2))
+
+- Add docs and cleanup matchingLabels ([commit](https://github.com/Polymer/polymer/commit/e1df1662))
+
+- Add tests ([commit](https://github.com/Polymer/polymer/commit/70edf1f8))
+
+- update types ([commit](https://github.com/Polymer/polymer/commit/2d674e75))
+
+- fix tests and add dependency import ([commit](https://github.com/Polymer/polymer/commit/a37ba7e2))
+
+- fix typings ([commit](https://github.com/Polymer/polymer/commit/8f8135b2))
+
+- Ensure DisableUpgradeMixin extends PropertiesMixin ([commit](https://github.com/Polymer/polymer/commit/7e74e363))
+
+- Format comment and remove deduping mixin ([commit](https://github.com/Polymer/polymer/commit/b8c66ded))
+
+- update types ([commit](https://github.com/Polymer/polymer/commit/1fd5f9cf))
+
+- update types ([commit](https://github.com/Polymer/polymer/commit/5bc45ce3))
+
+- Add mixin to automatically detect capitalized HTML attributes ([commit](https://github.com/Polymer/polymer/commit/37fd5ffe))
+
+- Add instructions for locally viewing the source documentation ([commit](https://github.com/Polymer/polymer/commit/206d3610))
+
+- Simplify condition checking in stylesFromModule function ([commit](https://github.com/Polymer/polymer/commit/e6903821))
+
+- Bump type generator and generate new typings. (#5119) ([commit](https://github.com/Polymer/polymer/commit/5c027309))
+
+- dispatchEvent returns boolean (#5117) ([commit](https://github.com/Polymer/polymer/commit/9d86135c))
+
+- Update types ([commit](https://github.com/Polymer/polymer/commit/63e7bbc7))
+
+- Fix license links ([commit](https://github.com/Polymer/polymer/commit/f3939875))
+
+- Fix issue with not genering the Templatizer docs ([commit](https://github.com/Polymer/polymer/commit/55708acf))
+
+- Bump TS type generator to pick up transitive mixin handling. ([commit](https://github.com/Polymer/polymer/commit/c3dad540))
+
+- Remove unnecessary mutableData property from MutableData mixin ([commit](https://github.com/Polymer/polymer/commit/92b83249))
+
+- Update types ([commit](https://github.com/Polymer/polymer/commit/868fba7c))
+
+- Add note to updateStyles regarding updates to CSS mixins ([commit](https://github.com/Polymer/polymer/commit/d458bab3))
+
+- Avoid timing issues with polyfilled Promise ([commit](https://github.com/Polymer/polymer/commit/6b3e007e))
+
+- Revert use of async/await due to lack of build/serve support. ([commit](https://github.com/Polymer/polymer/commit/d4a7a45b))
+
+- Revert types. ([commit](https://github.com/Polymer/polymer/commit/dea90802))
+
+- Update eslint parserOptions to es2017 for async/await support. ([commit](https://github.com/Polymer/polymer/commit/ef579e29))
+
+- Use stronger check for PropertyEffects clients. Fixes #5017 ([commit](https://github.com/Polymer/polymer/commit/e6d558ec))
+
+- Remove unneeded file ([commit](https://github.com/Polymer/polymer/commit/a5393b6d))
+
+- [PropertiesChanged]: allow old data to be gc'd after `_propertiesChanged` ([commit](https://github.com/Polymer/polymer/commit/74907b9a))
+
+- Update package-lock.json ([commit](https://github.com/Polymer/polymer/commit/c58f3e0d))
+
+- Make Travis update-types failure style the same as the elements. ([commit](https://github.com/Polymer/polymer/commit/8189382d))
+
+- Bump TypeScript generator version. ([commit](https://github.com/Polymer/polymer/commit/3e432190))
+
+- Make EventApi.path EventTarget type non-nullable. ([commit](https://github.com/Polymer/polymer/commit/3ede9b51))
+
+- Lint and type fixes ([commit](https://github.com/Polymer/polymer/commit/5607a2d8))
+
+- [PropertiesChanged]: adds _shouldPropertiesChange ([commit](https://github.com/Polymer/polymer/commit/c1885a6a))
+
+- Update docs: templatize() cannot be called multiple times ([commit](https://github.com/Polymer/polymer/commit/27fc21c5))
+
+- [ci skip] update changelog ([commit](https://github.com/Polymer/polymer/commit/65b4df86))
+
+- Update types. ([commit](https://github.com/Polymer/polymer/commit/c3b6236a))
+
+- Fix JSDoc example formatting ([commit](https://github.com/Polymer/polymer/commit/699cd87f))
+
+- Use latest webcomponents polyfill bundle ([commit](https://github.com/Polymer/polymer/commit/8fef6776))
+
+- Fix label tap by checking matched label pairs ([commit](https://github.com/Polymer/polymer/commit/a77d64e5))
+
+- Defer creation related work via `disable-upgrade` ([commit](https://github.com/Polymer/polymer/commit/a7eb9754))
+
+- lint fixes ([commit](https://github.com/Polymer/polymer/commit/de0ac5a2))
+
+- Adds `Polymer.DisableUpgradeMixin` ([commit](https://github.com/Polymer/polymer/commit/62ce3148))
+
 ## [v2.5.0](https://github.com/Polymer/polymer/tree/v2.5.0) (2018-02-02)
 - Update types ([commit](https://github.com/Polymer/polymer/commit/5fa059fa))
 
diff --git a/externs/closure-types.js b/externs/closure-types.js
index 53a27aed29..8e7f3dd19a 100644
--- a/externs/closure-types.js
+++ b/externs/closure-types.js
@@ -105,9 +105,10 @@ Polymer_PropertiesChanged.prototype._shouldPropertyChange = function(property, v
 * @param {string} name Name of attribute that changed
 * @param {?string} old Old attribute value
 * @param {?string} value New attribute value
+* @param {?string} namespace Attribute namespace.
 * @return {void}
 */
-Polymer_PropertiesChanged.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_PropertiesChanged.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @param {string} attribute Name of attribute to deserialize.
 * @param {?string} value of the attribute.
@@ -972,9 +973,10 @@ Polymer_LegacyElementMixin.prototype._initializeProperties = function(){};
 * @param {string} name Name of attribute.
 * @param {?string} old Old value of attribute.
 * @param {?string} value Current value of attribute.
+* @param {?string} namespace Attribute namespace.
 * @return {void}
 */
-Polymer_LegacyElementMixin.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_LegacyElementMixin.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @override
 * @return {void}
@@ -1402,7 +1404,7 @@ Polymer_DisableUpgradeMixin.prototype._enableProperties = function(){};
 /**
 * @override
 */
-Polymer_DisableUpgradeMixin.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_DisableUpgradeMixin.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @override
 */
diff --git a/lib/elements/dom-module.html b/lib/elements/dom-module.html
index 3ca593b1a9..01aad394c8 100644
--- a/lib/elements/dom-module.html
+++ b/lib/elements/dom-module.html
@@ -74,17 +74,20 @@
       return null;
     }
 
+    /* eslint-disable no-unused-vars */
     /**
      * @param {string} name Name of attribute.
      * @param {?string} old Old value of attribute.
      * @param {?string} value Current value of attribute.
+     * @param {?string} namespace Attribute namespace.
      * @return {void}
      */
-    attributeChangedCallback(name, old, value) {
+    attributeChangedCallback(name, old, value, namespace) {
       if (old !== value) {
         this.register();
       }
     }
+    /* eslint-enable no-unused-args */
 
     /**
      * The absolute URL of the original location of this `dom-module`.
diff --git a/lib/legacy/legacy-element-mixin.html b/lib/legacy/legacy-element-mixin.html
index 7306c65140..6c2045f155 100644
--- a/lib/legacy/legacy-element-mixin.html
+++ b/lib/legacy/legacy-element-mixin.html
@@ -137,12 +137,13 @@
        * @param {string} name Name of attribute.
        * @param {?string} old Old value of attribute.
        * @param {?string} value Current value of attribute.
+       * @param {?string} namespace Attribute namespace.
        * @return {void}
        * @override
        */
-      attributeChangedCallback(name, old, value) {
+      attributeChangedCallback(name, old, value, namespace) {
         if (old !== value) {
-          super.attributeChangedCallback(name, old, value);
+          super.attributeChangedCallback(name, old, value, namespace);
           this.attributeChanged(name, old, value);
         }
       }
diff --git a/lib/mixins/disable-upgrade-mixin.html b/lib/mixins/disable-upgrade-mixin.html
index a94418214e..f714325de5 100644
--- a/lib/mixins/disable-upgrade-mixin.html
+++ b/lib/mixins/disable-upgrade-mixin.html
@@ -60,13 +60,13 @@
       }
 
       /** @override */
-      attributeChangedCallback(name, old, value) {
+      attributeChangedCallback(name, old, value, namespace) {
         if (name == DISABLED_ATTR) {
           if (!this.__dataEnabled && value == null && this.isConnected) {
             super.connectedCallback();
           }
         } else {
-          super.attributeChangedCallback(name, old, value);
+          super.attributeChangedCallback(name, old, value, namespace);
         }
       }
 
@@ -113,4 +113,4 @@
 
 })();
 
-</script>
\ No newline at end of file
+</script>
diff --git a/lib/mixins/element-mixin.html b/lib/mixins/element-mixin.html
index 777db15243..d83946cef2 100644
--- a/lib/mixins/element-mixin.html
+++ b/lib/mixins/element-mixin.html
@@ -311,9 +311,9 @@
           } else {
             template = template.cloneNode(true);
           }
-          this.prototype._template = template;
         }
 
+        this.prototype._template = template;
       }
 
       /**
diff --git a/lib/mixins/properties-changed.html b/lib/mixins/properties-changed.html
index 000c1374af..cfde2854cc 100644
--- a/lib/mixins/properties-changed.html
+++ b/lib/mixins/properties-changed.html
@@ -407,15 +407,16 @@
          * @param {string} name Name of attribute that changed
          * @param {?string} old Old attribute value
          * @param {?string} value New attribute value
+         * @param {?string} namespace Attribute namespace.
          * @return {void}
          * @suppress {missingProperties} Super may or may not implement the callback
          */
-        attributeChangedCallback(name, old, value) {
+        attributeChangedCallback(name, old, value, namespace) {
           if (old !== value) {
             this._attributeToProperty(name, value);
           }
           if (super.attributeChangedCallback) {
-            super.attributeChangedCallback(name, old, value);
+            super.attributeChangedCallback(name, old, value, namespace);
           }
         }
 
diff --git a/lib/mixins/property-effects.html b/lib/mixins/property-effects.html
index 827c6de1a9..0feb7c9e41 100644
--- a/lib/mixins/property-effects.html
+++ b/lib/mixins/property-effects.html
@@ -43,6 +43,9 @@
     READ_ONLY: '__readOnly'
   };
 
+  /** @const {string} */
+  const capitalAttributeRegex = /[A-Z]/;
+
   /**
    * @typedef {{
    * name: (string | undefined),
@@ -2535,7 +2538,12 @@
           // Attribute or property
           let origName = name;
           let kind = 'property';
-          if (name[name.length-1] == '$') {
+          // The only way we see a capital letter here is if the attr has
+          // a capital letter in it per spec. In this case, to make sure
+          // this binding works, we go ahead and make the binding to the attribute.
+          if (capitalAttributeRegex.test(name)) {
+            kind = 'attribute';
+          } else if (name[name.length-1] == '$') {
             name = name.slice(0, -1);
             kind = 'attribute';
           }
diff --git a/lib/utils/boot.html b/lib/utils/boot.html
index ba85297eb5..0426caa656 100644
--- a/lib/utils/boot.html
+++ b/lib/utils/boot.html
@@ -49,7 +49,7 @@
   };
   /* eslint-enable */
 
-  window.Polymer.version = '2.5.0';
+  window.Polymer.version = '2.6.0';
 
   /* eslint-disable no-unused-vars */
   /*
diff --git a/lib/utils/debounce.html b/lib/utils/debounce.html
index 8344af328f..1507faa20a 100644
--- a/lib/utils/debounce.html
+++ b/lib/utils/debounce.html
@@ -113,6 +113,7 @@
     }
   }
 
+  /** @const */
   Polymer.Debouncer = Debouncer;
 })();
 </script>
diff --git a/lib/utils/style-gather.html b/lib/utils/style-gather.html
index 5c4fa8ceb6..3b0a48da6a 100644
--- a/lib/utils/style-gather.html
+++ b/lib/utils/style-gather.html
@@ -123,7 +123,9 @@
           // other dom-modules that contain styling
           let include = e.getAttribute(INCLUDE_ATTR);
           if (include) {
-            styles.push(...this.stylesFromModules(include));
+            styles.push(...this.stylesFromModules(include).filter(function(item, index, self) {
+              return self.indexOf(item) === index;
+            }));
           }
           if (baseURI) {
             e.textContent = Polymer.ResolveUrl.resolveCss(e.textContent, baseURI);
diff --git a/package-lock.json b/package-lock.json
index 5512cf0f9f..ebb58f4e7a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "@polymer/polymer",
-  "version": "2.5.0",
+  "version": "2.6.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 354e0f544d..6dd76ec68c 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@polymer/polymer",
-  "version": "2.5.0",
+  "version": "2.6.0",
   "description": "The Polymer library makes it easy to create your own web components. Give your element some markup and properties, and then use it on a site. Polymer provides features like dynamic templates and data binding to reduce the amount of boilerplate you need to write",
   "main": "polymer.html",
   "directories": {
diff --git a/test/smoke/behavior-mixin.html b/test/smoke/behavior-mixin.html
index 6c9ed28d7b..b604821080 100644
--- a/test/smoke/behavior-mixin.html
+++ b/test/smoke/behavior-mixin.html
@@ -22,6 +22,7 @@
   </template>
 </dom-module>
 <script>
+  /** @polymerBehavior */
   var MyBehavior = {
     properties: {
       behaviorProp: {
@@ -37,6 +38,7 @@
     }
   }
 
+  /** @polymerBehavior */
   var MyBehavior2 = {
     ready: function() {
       console.log(this.localName, 'MyBehavior2.ready');
diff --git a/test/unit/inheritance.html b/test/unit/inheritance.html
index 25c8910427..be78f49ca3 100644
--- a/test/unit/inheritance.html
+++ b/test/unit/inheritance.html
@@ -113,6 +113,24 @@
     </script>
   </dom-module>
 
+  <dom-module id="parent-element-template-overriding">
+    <script>
+    HTMLImports.whenReady(function() {
+      class ParentElementWithTemplate extends Polymer.Element {
+        static get template() {
+          return Polymer.html`This template should not exist`;
+        }
+      }
+      class ChildWithNoTemplate extends ParentElementWithTemplate {
+        static get template() {
+          return null;
+        }
+      }
+      customElements.define('child-with-no-template', ChildWithNoTemplate);
+    });
+    </script>
+  </dom-module>
+
   <test-fixture id="basic">
     <template>
       <base-el></base-el>
@@ -237,6 +255,23 @@
       assert.equal(child.handleCustomEvent.callCount, 1);
     });
   });
+
+  suite('child overriding a template', function() {
+    let el;
+
+    setup(function() {
+      el = document.createElement('child-with-no-template');
+      document.body.appendChild(el);
+    });
+
+    teardown(function() {
+      document.body.removeChild(el);
+    });
+
+    test('returning null nullifies the parent template', function() {
+      assert.equal(el.shadowRoot, null);
+    });
+  });
   </script>
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/test/unit/property-effects-elements.html b/test/unit/property-effects-elements.html
index 2e3efbc0b7..f9144d74f1 100644
--- a/test/unit/property-effects-elements.html
+++ b/test/unit/property-effects-elements.html
@@ -7,7 +7,9 @@
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
+<link rel="import" href="../../polymer.html">
 <link rel="import" href="../../lib/mixins/strict-binding-parser.html">
+
 <dom-module id="x-basic">
   <template>
     <div id="boundChild"
@@ -1084,3 +1086,23 @@
 }
 customElements.define(SubObserverElement.is, SubObserverElement);
 </script>
+
+<dom-module id="svg-element">
+  <template>
+    <svg id="svg" viewBox="[[value]]"></svg>
+  </template>
+  <script>
+    class SVGElement extends Polymer.Element {
+      static get is() { return 'svg-element'; }
+      static get properties() {
+        return {
+          value: {
+            type: String,
+            value: '0 0 50 50'
+          }
+        };
+      }
+    }
+    customElements.define(SVGElement.is, SVGElement);
+  </script>
+</dom-module>
diff --git a/test/unit/property-effects.html b/test/unit/property-effects.html
index fbb8ac7fbe..d4ed2e4442 100644
--- a/test/unit/property-effects.html
+++ b/test/unit/property-effects.html
@@ -427,6 +427,23 @@
     });
   });
 
+  suite('automated attribute capitalization detection', function() {
+    let el;
+
+    setup(function() {
+      el = document.createElement('svg-element');
+      document.body.appendChild(el);
+    });
+
+    teardown(function() {
+      document.body.removeChild(el);
+    });
+
+    test('can handle capitalized HTML attribute', function() {
+      assert.equal(el.$.svg.getAttribute('viewBox'), el.value);
+    });
+  });
+
   suite('can work with strict binding parser', function() {
     setup(function() {
       document.body.removeChild(el);
diff --git a/test/unit/styling-scoped.html b/test/unit/styling-scoped.html
index aefc3891f7..47b63d85e7 100644
--- a/test/unit/styling-scoped.html
+++ b/test/unit/styling-scoped.html
@@ -729,6 +729,37 @@
     </script>
   </dom-module>
 
+  <dom-module id="double-shared-style">
+    <template>
+      <style>
+        .double-shared-style {
+          color: green;
+        }
+      </style>
+    </template>
+  </dom-module>
+
+  <dom-module id="importing-double-shared-style">
+    <template>
+      <style include="double-shared-style">
+      </style>
+    </template>
+  </dom-module>
+
+  <dom-module id="double-shared-styling-element">
+    <template>
+      <style include="importing-double-shared-style double-shared-style"></style>
+    </template>
+    <script>
+    HTMLImports.whenReady(() => {
+      class DoubleSharedStylingElement extends Polymer.Element {
+        static get is() { return 'double-shared-styling-element'; }
+      }
+      customElements.define(DoubleSharedStylingElement.is, DoubleSharedStylingElement);
+    });
+    </script>
+  </dom-module>
+
 <script>
 (function() {
   function assertComputed(element, value, property, pseudo) {
@@ -1012,6 +1043,38 @@
 
   });
 
+  suite('double including style sheets', function() {
+    let el;
+
+    setup(function() {
+      el = document.createElement('double-shared-styling-element');
+      document.body.appendChild(el);
+    });
+
+    teardown(function() {
+      document.body.removeChild(el);
+    });
+
+    test('only includes style modules once', function() {
+      const style = el.shadowRoot.querySelector('style');
+
+      // We cant use the regular "does a sub-node have the correct style",
+      // because we actually need to assert on the actual style content.
+      // In native shadow dom, the style element resides in the shadowRoot,
+      // but in shadyDOM it has moved to the head and the selector has been altered.
+      if (style) {
+        assert.equal(style.textContent, `.double-shared-style {
+  color: green;
+}`, 'There should be only one class selector in this style element');
+      } else {
+        assert.equal(document.head.querySelector('[scope="double-shared-styling-element"]').textContent,
+`.double-shared-style.double-shared-styling-element {
+  color: green;
+}`);
+      }
+    });
+  });
+
   if (window.ShadyDOM) {
 
     suite('scoped-styling-shady-only', function() {
diff --git a/types/lib/elements/dom-module.d.ts b/types/lib/elements/dom-module.d.ts
index 7229968d42..e745986b7f 100644
--- a/types/lib/elements/dom-module.d.ts
+++ b/types/lib/elements/dom-module.d.ts
@@ -63,8 +63,9 @@ declare namespace Polymer {
      * @param name Name of attribute.
      * @param old Old value of attribute.
      * @param value Current value of attribute.
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Registers the dom-module at a given id. This method should only be called
diff --git a/types/lib/legacy/legacy-element-mixin.d.ts b/types/lib/legacy/legacy-element-mixin.d.ts
index cfe9164678..e28fd84f68 100644
--- a/types/lib/legacy/legacy-element-mixin.d.ts
+++ b/types/lib/legacy/legacy-element-mixin.d.ts
@@ -63,8 +63,9 @@ declare namespace Polymer {
      * @param name Name of attribute.
      * @param old Old value of attribute.
      * @param value Current value of attribute.
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Provides an implementation of `connectedCallback`
diff --git a/types/lib/mixins/disable-upgrade-mixin.d.ts b/types/lib/mixins/disable-upgrade-mixin.d.ts
index f8584219d8..858b4a1e7d 100644
--- a/types/lib/mixins/disable-upgrade-mixin.d.ts
+++ b/types/lib/mixins/disable-upgrade-mixin.d.ts
@@ -42,7 +42,7 @@ declare namespace Polymer {
   interface DisableUpgradeMixin {
     _initializeProperties(): void;
     _enableProperties(): void;
-    attributeChangedCallback(name: any, old: any, value: any): void;
+    attributeChangedCallback(name: any, old: any, value: any, namespace: any): void;
     connectedCallback(): void;
     disconnectedCallback(): void;
   }
diff --git a/types/lib/mixins/properties-changed.d.ts b/types/lib/mixins/properties-changed.d.ts
index 13364e1980..0c074275bd 100644
--- a/types/lib/mixins/properties-changed.d.ts
+++ b/types/lib/mixins/properties-changed.d.ts
@@ -235,8 +235,9 @@ declare namespace Polymer {
      * @param name Name of attribute that changed
      * @param old Old attribute value
      * @param value New attribute value
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Deserializes an attribute to its associated property.