diff --git a/src/querySelector.js b/src/querySelector.js
index f1da41e..900ef95 100644
--- a/src/querySelector.js
+++ b/src/querySelector.js
@@ -5,6 +5,9 @@
 (function(scope) {
   'use strict';
 
+  var HTMLCollection = scope.wrappers.HTMLCollection;
+  var NodeList = scope.wrappers.NodeList;
+
   function findOne(node, selector) {
     var m, el = node.firstElementChild;
     while (el) {
@@ -18,15 +21,46 @@
     return null;
   }
 
-  function findAll(node, selector, results) {
+  function matchesSelector(el, selector) {
+    return el.matches(selector);
+  }
+
+  var XHTML_NS = 'http://www.w3.org/1999/xhtml';
+
+  function matchesTagName(el, localName, localNameLowerCase) {
+    if (localName === '*')
+      return true;
+
+    var ln = el.localName;
+    return ln === localName ||
+        ln === localNameLowerCase && el.namespaceURI === XHTML_NS;
+  }
+
+  function matchesEveryThing() {
+    return true;
+  }
+
+  function matchesLocalName(el, localName) {
+    return el.localName === localName;
+  }
+
+  function matchesNameSpace(el, ns) {
+    return el.namespaceURI === ns;
+  }
+
+  function matchesLocalNameNS(el, ns, localName) {
+    return el.namespaceURI === ns && el.localName === localName;
+  }
+
+  function findElements(node, result, p, arg0, arg1) {
     var el = node.firstElementChild;
     while (el) {
-      if (el.matches(selector))
-        results[results.length++] = el;
-      findAll(el, selector, results);
+      if (p(el, arg0, arg1))
+        result[result.length++] = el;
+      findElements(el, result, p, arg0, arg1);
       el = el.nextElementSibling;
     }
-    return results;
+    return result;
   }
 
   // find and findAll will only match Simple Selectors,
@@ -38,32 +72,38 @@
       return findOne(this, selector);
     },
     querySelectorAll: function(selector) {
-      return findAll(this, selector, new NodeList())
+      return findElements(this, new NodeList(), matchesSelector, selector);
     }
   };
 
   var GetElementsByInterface = {
-    getElementsByTagName: function(tagName) {
-      // TODO(arv): Check tagName?
-      return this.querySelectorAll(tagName);
+    getElementsByTagName: function(localName) {
+      return findElements(this, new HTMLCollection(),
+          matchesTagName,
+          localName,
+          localName.toLowerCase());
     },
+
     getElementsByClassName: function(className) {
       // TODO(arv): Check className?
       return this.querySelectorAll('.' + className);
     },
-    getElementsByTagNameNS: function(ns, tagName) {
-      if (ns === '*')
-        return this.getElementsByTagName(tagName);
-
-      // TODO(arv): Check tagName?
-      var result = new NodeList;
-      var els = this.getElementsByTagName(tagName);
-      for (var i = 0, j = 0; i < els.length; i++) {
-        if (els[i].namespaceURI === ns)
-          result[j++] = els[i];
+
+    getElementsByTagNameNS: function(ns, localName) {
+      var result = new HTMLCollection();
+
+      if (ns === '') {
+        ns = null;
+      } else if (ns === '*') {
+        if (localName === '*')
+          return findElements(this, result, matchesEveryThing);
+        return findElements(this, result, matchesLocalName, localName);
       }
-      result.length = j;
-      return result;
+
+      if (localName === '*')
+        return findElements(this, result, matchesNameSpace, ns);
+
+      return findElements(this, result, matchesLocalNameNS, ns, localName);
     }
   };
 
diff --git a/test/js/Document.js b/test/js/Document.js
index a5afd72..41d1d6b 100644
--- a/test/js/Document.js
+++ b/test/js/Document.js
@@ -93,6 +93,10 @@ htmlSuite('Document', function() {
     var nsTwo = 'http://two.com';
     var aOne = div.appendChild(document.createElementNS(nsOne, 'a'));
     var aTwo = div.appendChild(document.createElementNS(nsTwo, 'a'));
+    var aNull = div.appendChild(document.createElementNS(null, 'a'));
+    var bOne = div.appendChild(document.createElementNS(nsOne, 'b'));
+    var bTwo = div.appendChild(document.createElementNS(nsTwo, 'b'));
+    var bNull = div.appendChild(document.createElementNS(null, 'b'));
 
     var all = div.getElementsByTagNameNS(nsOne, 'a');
     assert.equal(all.length, 1);
@@ -102,10 +106,36 @@ htmlSuite('Document', function() {
     assert.equal(all.length, 1);
     assert.equal(all[0], aTwo);
 
+    var all = div.getElementsByTagNameNS(null, 'a');
+    assert.equal(all.length, 1);
+    assert.equal(all[0], aNull);
+
+    var all = div.getElementsByTagNameNS('', 'a');
+    assert.equal(all.length, 1);
+    assert.equal(all[0], aNull);
+
     var all = div.getElementsByTagNameNS('*', 'a');
+    assert.equal(all.length, 3);
+    assert.equal(all[0], aOne);
+    assert.equal(all[1], aTwo);
+    assert.equal(all[2], aNull);
+
+    var all = div.getElementsByTagNameNS(nsOne, '*');
     assert.equal(all.length, 2);
     assert.equal(all[0], aOne);
+    assert.equal(all[1], bOne);
+
+    var all = div.getElementsByTagNameNS('*', '*');
+    assert.equal(all.length, 6);
+    assert.equal(all[0], aOne);
     assert.equal(all[1], aTwo);
+    assert.equal(all[2], aNull);
+    assert.equal(all[3], bOne);
+    assert.equal(all[4], bTwo);
+    assert.equal(all[5], bNull);
+
+    var all = div.getElementsByTagNameNS('*', 'A');
+    assert.equal(all.length, 0);
   });
 
   test('querySelectorAll', function() {
diff --git a/test/js/Element.js b/test/js/Element.js
index 8291716..f5a9c27 100644
--- a/test/js/Element.js
+++ b/test/js/Element.js
@@ -84,6 +84,49 @@ suite('Element', function() {
     assert.equal(as[1], a4);
   });
 
+  test('getElementsByTagName with colon', function() {
+    var div = document.createElement('div');
+    div.innerHTML = '<a:b:c>0</a:b:c><a:b:c>1</a:b:c>';
+    var a0 = div.firstChild;
+    var a1 = div.lastChild;
+
+    var as = div.getElementsByTagName('a:b:c');
+    assert.equal(as.length, 2);
+    assert.equal(as[0], a0);
+    assert.equal(as.item(0), a0);
+    assert.equal(as[1], a1);
+    assert.equal(as.item(1), a1);
+  });
+
+  test('getElementsByTagName with namespace', function() {
+    var div = document.createElement('div');
+    div.innerHTML = '<a>0</a><a>1</a>';
+    var a0 = div.firstChild;
+    var a1 = div.lastChild;
+    var a2 = document.createElementNS('NS', 'a');
+    var a3 = document.createElementNS('NS', 'A');
+    div.appendChild(a2);
+    div.appendChild(a3);
+
+    var as = div.getElementsByTagName('a');
+    assert.equal(as.length, 3);
+    assert.equal(as[0], a0);
+    assert.equal(as.item(0), a0);
+    assert.equal(as[1], a1);
+    assert.equal(as.item(1), a1);
+    assert.equal(as[2], a2);
+    assert.equal(as.item(2), a2);
+
+    var as = div.getElementsByTagName('A');
+    assert.equal(as.length, 3);
+    assert.equal(as[0], a0);
+    assert.equal(as.item(0), a0);
+    assert.equal(as[1], a1);
+    assert.equal(as.item(1), a1);
+    assert.equal(as[2], a3);
+    assert.equal(as.item(2), a3);
+  });
+
   test('getElementsByClassName', function() {
     var div = document.createElement('div');
     div.innerHTML = '<span class=a>0</span><span class=a>1</span>';