diff --git a/lib/chai/core/assertions.js b/lib/chai/core/assertions.js
index 959d210d7..61fa16c34 100644
--- a/lib/chai/core/assertions.js
+++ b/lib/chai/core/assertions.js
@@ -325,6 +325,29 @@ module.exports = function (chai, _) {
     );
   });
 
+  /**
+   * ### .defined
+   *
+   * Asserts that the target is not `undefined`.
+   *
+   *     expect(undefined).to.be.defined;
+   *     expect(null).to.not.be.defined;
+   *
+   * Needed because it is intuitive to invert .undefined,
+   * which would always pass if .defined is nonexistent.
+   *
+   * @name undefined
+   * @api public
+   */
+
+  Assertion.addProperty('defined', function () {
+    this.assert(
+        undefined !== flag(this, 'object')
+      , 'expected #{this} to be defined'
+      , 'expected #{this} not to be defined'
+    );
+  });
+
   /**
    * ### .exist
    *
diff --git a/test/expect.js b/test/expect.js
index d504a8eaf..91dbf1720 100644
--- a/test/expect.js
+++ b/test/expect.js
@@ -70,6 +70,17 @@ describe('expect', function () {
     }, "expected '' to be undefined")
   });
 
+  it("defined", function() {
+    expect({}).to.be.defined;
+    expect(function() {}).to.be.defined;
+    expect(false).to.be.defined;
+    expect(undefined).to.not.be.defined;
+
+    err(function(){
+      expect(undefined).to.be.defined;
+    }, "expected undefined to be defined");
+  });
+
   it('exist', function(){
     var foo = 'bar'
       , bar;