diff --git a/core/blockly.js b/core/blockly.js
index 15914fd79..4b85b99bf 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -341,6 +341,42 @@ Blockly.getMainWorkspace = function() {
   return Blockly.mainWorkspace;
 };
 
+/**
+ * Wrapper to window.alert() that app developers may override to 
+ * provide alternatives to the modal browser window.
+ * @param {string} message The message to display to the user.
+ * @param {function()=} opt_callback The callback when the alert is dismissed.
+ */
+Blockly.alert = function(message, opt_callback) {
+  window.alert(message);
+  if (opt_callback) {
+    opt_callback();
+  }
+};
+
+/**
+ * Wrapper to window.confirm() that app developers may override to 
+ * provide alternatives to the modal browser window.
+ * @param {string} message The message to display to the user.
+ * @param {!function(boolean)} callback The callback for handling user response.
+ */
+Blockly.confirm = function(message, callback) {
+  callback(window.confirm(message));
+};
+
+/**
+ * Wrapper to window.prompt() that app developers may override to provide
+ * alternatives to the modal browser window. Built-in browser prompts are
+ * often used for better text input experience on mobile device. We strongly
+ * recommend testing mobile when overriding this.
+ * @param {string} message The message to display to the user.
+ * @param {string} defaultValue The value to initialize the prompt with.
+ * @param {!function(string)} callback The callback for handling user reponse.
+ */
+Blockly.prompt = function(message, defaultValue, callback) {
+  callback(window.prompt(message, defaultValue));
+};
+
 // IE9 does not have a console.  Create a stub to stop errors.
 if (!goog.global['console']) {
   goog.global['console'] = {
diff --git a/core/field_angle.js b/core/field_angle.js
index 5bea3cbc1..1a303fcf4 100644
--- a/core/field_angle.js
+++ b/core/field_angle.js
@@ -130,7 +130,7 @@ Blockly.FieldAngle.prototype.showEditor_ = function() {
   Blockly.FieldAngle.superClass_.showEditor_.call(this, noFocus);
   var div = Blockly.WidgetDiv.DIV;
   if (!div.firstChild) {
-    // Mobile interface uses window.prompt.
+    // Mobile interface uses Blockly.prompt.
     return;
   }
   // Build the SVG DOM.
diff --git a/core/field_textinput.js b/core/field_textinput.js
index 5c057513f..8f3129eeb 100644
--- a/core/field_textinput.js
+++ b/core/field_textinput.js
@@ -114,11 +114,14 @@ Blockly.FieldTextInput.prototype.showEditor_ = function(opt_quietInput) {
   if (!quietInput && (goog.userAgent.MOBILE || goog.userAgent.ANDROID ||
                       goog.userAgent.IPAD)) {
     // Mobile browsers have issues with in-line textareas (focus & keyboards).
-    var newValue = window.prompt(Blockly.Msg.CHANGE_VALUE_TITLE, this.text_);
-    if (this.sourceBlock_) {
-      newValue = this.callValidator(newValue);
-    }
-    this.setValue(newValue);
+    var fieldText = this;
+    Blockly.prompt(Blockly.Msg.CHANGE_VALUE_TITLE, this.text_,
+      function(newValue) {
+        if (fieldText.sourceBlock_) {
+          newValue = fieldText.callValidator(newValue);
+        }
+        fieldText.setValue(newValue);
+      });
     return;
   }
 
diff --git a/core/variables.js b/core/variables.js
index 00c38ad21..35fb3139b 100644
--- a/core/variables.js
+++ b/core/variables.js
@@ -227,47 +227,57 @@ Blockly.Variables.generateUniqueName = function(workspace) {
  * Create a new variable on the given workspace.
  * @param {!Blockly.Workspace} workspace The workspace on which to create the
  *     variable.
- * @return {null|undefined|string} An acceptable new variable name, or null if
- *     change is to be aborted (cancel button), or undefined if an existing
- *     variable was chosen.
+ * @param {function(null|undefined|string)=} opt_callback A callback. It will
+ *     return an acceptable new variable name, or null if change is to be
+ *     aborted (cancel button), or undefined if an existing variable was chosen.
  */
-Blockly.Variables.createVariable = function(workspace) {
-  while (true) {
-    var text = Blockly.Variables.promptName(Blockly.Msg.NEW_VARIABLE_TITLE, '');
-    if (text) {
-      if (workspace.variableIndexOf(text) != -1) {
-        window.alert(Blockly.Msg.VARIABLE_ALREADY_EXISTS.replace('%1',
-            text.toLowerCase()));
-      } else {
-        workspace.createVariable(text);
-        break;
-      }
-    } else {
-      text = null;
-      break;
-    }
-  }
-  return text;
+Blockly.Variables.createVariable = function(workspace, opt_callback) {
+  var promptAndCheckWithAlert = function(defaultName) {
+    Blockly.Variables.promptName(Blockly.Msg.NEW_VARIABLE_TITLE, defaultName,
+      function(text) {
+        if (text) {
+          if (workspace.variableIndexOf(text) != -1) {
+            Blockly.alert(Blockly.Msg.VARIABLE_ALREADY_EXISTS.replace('%1',
+                text.toLowerCase()),
+                function() {
+                  promptAndCheckWithAlert(text);  // Recurse
+                });
+          } else {
+            workspace.createVariable(text);
+            if (opt_callback) {
+              opt_callback(text);
+            }
+          }
+        } else {
+          // User canceled prompt without a value.
+          if (opt_callback) {
+            opt_callback(null);
+          }
+        }
+      });
+  };
+  promptAndCheckWithAlert('');
 };
 
 /**
  * Prompt the user for a new variable name.
  * @param {string} promptText The string of the prompt.
  * @param {string} defaultText The default value to show in the prompt's field.
- * @return {?string} The new variable name, or null if the user picked
- *     something illegal.
+ * @param {function(?string)} callback A callback. It will return the new
+ *     variable name, or null if the user picked something illegal.
  */
-Blockly.Variables.promptName = function(promptText, defaultText) {
-  var newVar = window.prompt(promptText, defaultText);
-  // Merge runs of whitespace.  Strip leading and trailing whitespace.
-  // Beyond this, all names are legal.
-  if (newVar) {
-    newVar = newVar.replace(/[\s\xa0]+/g, ' ').replace(/^ | $/g, '');
-    if (newVar == Blockly.Msg.RENAME_VARIABLE ||
-        newVar == Blockly.Msg.NEW_VARIABLE) {
-      // Ok, not ALL names are legal...
-      newVar = null;
+Blockly.Variables.promptName = function(promptText, defaultText, callback) {
+  Blockly.prompt(promptText, defaultText, function(newVar) {
+    // Merge runs of whitespace.  Strip leading and trailing whitespace.
+    // Beyond this, all names are legal.
+    if (newVar) {
+      newVar = newVar.replace(/[\s\xa0]+/g, ' ').replace(/^ | $/g, '');
+      if (newVar == Blockly.Msg.RENAME_VARIABLE ||
+          newVar == Blockly.Msg.NEW_VARIABLE) {
+        // Ok, not ALL names are legal...
+        newVar = null;
+      }
     }
-  }
-  return newVar;
+    callback(newVar);
+  });
 };
diff --git a/core/workspace.js b/core/workspace.js
index 805790869..5cf916571 100644
--- a/core/workspace.js
+++ b/core/workspace.js
@@ -309,26 +309,29 @@ Blockly.Workspace.prototype.deleteVariable = function(name) {
         if (block.type == 'procedures_defnoreturn' ||
           block.type == 'procedures_defreturn') {
           var procedureName = block.getFieldValue('NAME');
-          window.alert(
+          Blockly.alert(
               Blockly.Msg.CANNOT_DELETE_VARIABLE_PROCEDURE.replace('%1', name).
-              replace('%2', procedureName));
+                  replace('%2', procedureName));
           return;
         }
       }
-      var ok = window.confirm(
+      var workspace = this;
+      Blockly.confirm(
           Blockly.Msg.DELETE_VARIABLE_CONFIRMATION.replace('%1', uses.length).
-          replace('%2', name));
-      if (!ok) {
-        return;
-      }
-    }
+          replace('%2', name),
+          function(ok) {
+            if (!ok) {
+              return;
+            }
 
-    Blockly.Events.setGroup(true);
-    for (var i = 0; i < uses.length; i++) {
-      uses[i].dispose(true, false);
+            Blockly.Events.setGroup(true);
+            for (var i = 0; i < uses.length; i++) {
+              uses[i].dispose(true, false);
+            }
+            Blockly.Events.setGroup(false);
+            workspace.variableList.splice(variableIndex, 1);
+          });
     }
-    Blockly.Events.setGroup(false);
-    this.variableList.splice(variableIndex, 1);
   }
 };
 
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 24797f93b..fe2ad54bd 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -998,10 +998,16 @@ Blockly.WorkspaceSvg.prototype.showContextMenu_ = function(e) {
         Blockly.Msg.DELETE_X_BLOCKS.replace('%1', String(deleteList.length)),
     enabled: deleteList.length > 0,
     callback: function() {
-      if (deleteList.length < 2 ||
-          window.confirm(Blockly.Msg.DELETE_ALL_BLOCKS.replace('%1',
-          String(deleteList.length)))) {
+      if (deleteList.length < 2 ) {
         deleteNext();
+      } else {
+        Blockly.confirm(Blockly.Msg.DELETE_ALL_BLOCKS.
+            replace('%1',String(deleteList.length)),
+            function(ok) {
+              if (ok) {
+                deleteNext();
+              }
+            });
       }
     }
   };
diff --git a/demos/custom-dialogs/custom-dialog.js b/demos/custom-dialogs/custom-dialog.js
new file mode 100644
index 000000000..77a79660a
--- /dev/null
+++ b/demos/custom-dialogs/custom-dialog.js
@@ -0,0 +1,163 @@
+/**
+ * Blockly Demos: Custom Dialogs
+ *
+ * Copyright 2016 Google Inc.
+ * https://developers.google.com/blockly/
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CustomDialog = {}
+
+/** Override Blockly.alert() with custom implementation. */
+Blockly.alert = function(message, callback) {
+    console.log('Alert: ' + message);
+    CustomDialog.show('Alert', message, {
+        onCancel: callback
+    });
+};
+
+/** Override Blockly.confirm() with custom implementation. */
+Blockly.confirm = function(message, callback) {
+    console.log('Confirm: ' + message);
+    CustomDialog.show('Confirm', message, {
+        showOkay: true,
+        onOkay: function() {
+            callback(true)
+        },
+        showCancel: true,
+        onCancel: function() {
+            callback(false)
+        }
+    });
+};
+
+/** Override Blockly.prompt() with custom implementation. */
+Blockly.prompt = function(message, defaultValue, callback) {
+    console.log('Prompt: ' + message);
+    CustomDialog.show('Prompt', message, {
+        showInput: true,
+        showOkay: true,
+        onOkay: function() {
+            callback(CustomDialog.inputField.value)
+        },
+        showCancel: true,
+        onCancel: function() {
+            callback(null)
+        }
+    });
+    CustomDialog.inputField.value = defaultValue;
+};
+
+
+CustomDialog.hide = function() {
+    if (CustomDialog.backdropDiv_) {
+        CustomDialog.backdropDiv_.style.display = 'none'
+        CustomDialog.dialogDiv_.style.display = 'none'
+    }
+}
+
+/**
+ * Shows the dialog.
+ * Allowed options:
+ *  - showOkay: Whether to show the OK button.
+ *  - showCancel: Whether to show the Cancel button.
+ *  - showInput: Whether to show the text input field.
+ *  - onOkay: Callback to handle the okay button.
+ *  - onCancel: Callback to handle the cancel button.
+ */
+CustomDialog.show = function(title, message, options) {
+    var backdropDiv = CustomDialog.backdropDiv_;
+    var dialogDiv = CustomDialog.dialogDiv_;
+    if (!dialogDiv) {
+        // Generate HTML
+        var body = document.getElementsByTagName('body')[0];
+        backdropDiv = document.createElement('div');
+        backdropDiv.setAttribute('id', 'backdrop');
+        backdropDiv.style.cssText =
+              'position: absolute;'
+              + 'top: 0px;'
+              + 'left: 0px;'
+              + 'right: 0px;'
+              + 'bottom: 0px;'
+              + 'background-color: rgba(0, 0, 0, 0.7);';
+        body.appendChild(backdropDiv);
+
+        dialogDiv = document.createElement('div');
+        dialogDiv.setAttribute('id', 'dialog');
+        dialogDiv.style.cssText =
+                'background-color: white;'
+                + 'width: 400px;'
+                + 'margin: 20px auto 0;'
+                + 'padding: 10px;';
+        backdropDiv.appendChild(dialogDiv);
+
+        dialogDiv.onclick = function(event) {
+            event.stopPropagation();
+        };
+
+        CustomDialog.backdropDiv_ = backdropDiv;
+        CustomDialog.dialogDiv_ = dialogDiv;
+    }
+    backdropDiv.style.display = 'block';
+    dialogDiv.style.display = 'block';
+
+    dialogDiv.innerHTML = '<div id="dialogTitle"><strong>' + title + '</strong></div>'
+            + '<p>' + message + '</p>'
+            + (options.showInput? '<div><input id="dialogInput"></div>' : '')
+            + '<div class="buttons">'
+            + (options.showCancel ? '<button id="dialogCancel">Cancel</button>': '')
+            + (options.showOkay ? '<button id="dialogOkay">OK</button>': '')
+            + '</div>';
+
+    var onOkay = function(event) {
+        CustomDialog.hide();
+        options.onOkay && options.onOkay();
+        event && event.stopPropagation();
+    };
+    var onCancel = function(event) {
+        CustomDialog.hide();
+        options.onCancel && options.onCancel();
+        event && event.stopPropagation();
+    };
+
+    var dialogInput = document.getElementById('dialogInput');
+    CustomDialog.inputField = dialogInput;
+    if (dialogInput) {
+        dialogInput.focus();
+
+        dialogInput.onkeyup = function(event) {
+            if (event.keyCode == 13) {
+                // Process as OK when user hits enter.
+                onOkay();
+                return false;
+            } else if (event.keyCode == 27)  {
+                // Process as cancel when user hits esc.
+                onCancel();
+                return false;
+            }
+        };
+    } else {
+        var okay = document.getElementById('dialogOkay');
+        okay && okay.focus();
+    }
+
+    if (options.showOkay) {
+        document.getElementById('dialogOkay').onclick = onOkay;
+    }
+    if (options.showCancel) {
+        document.getElementById('dialogCancel').onclick = onCancel;
+    }
+
+    backdropDiv.onclick = onCancel;
+}
diff --git a/demos/custom-dialogs/index.html b/demos/custom-dialogs/index.html
new file mode 100644
index 000000000..42cba5477
--- /dev/null
+++ b/demos/custom-dialogs/index.html
@@ -0,0 +1,57 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Blockly Demo: Custom Dialog</title>
+  <script src="../../blockly_compressed.js"></script>
+  <script src="../../blocks_compressed.js"></script>
+  <script src="../../msg/js/en.js"></script>
+  <style>
+    body {
+      background-color: #fff;
+      font-family: sans-serif;
+    }
+    h1 {
+      font-weight: normal;
+      font-size: 140%;
+    }
+  </style>
+</head>
+<body>
+  <h1><a href="https://developers.google.com/blockly/">Blockly</a> &gt;
+    <a href="../index.html">Demos</a> &gt; Custom Dialog</h1>
+
+  <p>This is a simple demo of replacing modal browser dialogs with HTML.</p>
+
+  <p>Try creating new variables, creating variables with names already in
+     use, or deleting multiple blocks on the workspace.
+  </p>
+
+  <div id="blocklyDiv" style="height: 480px; width: 600px;"></div>
+
+  <xml id="toolbox" style="display: none">
+    <category name="Inputs" colour="230">
+      <block type="math_number" gap="32"></block>
+      <block type="text"></block>
+      <block type="text_prompt_ext">
+        <value name="TEXT">
+          <shadow type="text">
+            <field name="TEXT">abc</field>
+          </shadow>
+        </value>
+      </block>
+    </category>
+    <sep></sep>
+    <category name="Variables" colour="330" custom="VARIABLE"></category>
+    <category name="Functions" colour="290" custom="PROCEDURE"></category>
+  </xml>
+
+  <script>
+    var workspace = Blockly.inject('blocklyDiv',
+        {media: '../../media/',
+         toolbox: document.getElementById('toolbox')});
+  </script>
+  <script src="custom-dialog.js"></script>
+
+</body>
+</html>