diff --git a/lib/class.js b/lib/class.js
index b0af43c..cd3c047 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -34,6 +34,16 @@ var util           = require( './util' ),
  */
 var class_meta = {};
 
+/**
+ * Stores class instance visibility object
+ *
+ * For each instance id, an object exists that contains the private and
+ * protected members.
+ *
+ * @type {Object.<number, Object>}
+ */
+var class_instance = {};
+
 
 /**
  * Creates a class, inheriting either from the provided base class or the
@@ -188,7 +198,8 @@ function Class() {};
  */
 var extend = ( function( extending )
 {
-    var class_id = 0;
+    var class_id    = 0,
+        instance_id = 0;
 
     /**
      * Mimics class inheritance
@@ -215,8 +226,8 @@ var extend = ( function( extending )
             hasOwn = Array.prototype.hasOwnProperty;
 
         var properties = {},
-            members    = member_builder.initMembers( prototype ),
             prop_init  = member_builder.initMembers(),
+            members    = member_builder.initMembers( prototype ),
 
             abstract_methods =
                 util.clone( getMeta( base.__cid ).abstractMethods )
@@ -261,7 +272,7 @@ var extend = ( function( extending )
             method: function( name, func, is_abstract, keywords )
             {
                 member_builder.buildMethod(
-                    members, null, name, func, keywords
+                    members, null, name, func, keywords, getMethodInstance
                 );
 
                 if ( is_abstract )
@@ -294,7 +305,7 @@ var extend = ( function( extending )
         // set up the new class
         var new_class = createCtor( abstract_methods );
 
-        attachPropInit( prototype, prop_init );
+        attachPropInit( prototype, prop_init, members );
 
         new_class.prototype   = prototype;
         new_class.constructor = new_class;
@@ -334,6 +345,7 @@ var extend = ( function( extending )
         {
             var args = null;
 
+            // constructor function to be returned
             var __self = function()
             {
                 if ( !( this instanceof __self ) )
@@ -344,6 +356,10 @@ var extend = ( function( extending )
                     return new __self();
                 }
 
+                // generate and store unique instance id
+                attachInstanceId( this, ++instance_id, __self );
+
+                initInstance( instance_id, this );
                 this.__initProps();
 
                 // call the constructor, if one was provided
@@ -455,6 +471,29 @@ function setupProps( func, abstract_methods, class_id )
 }
 
 
+/**
+ * Initializes class instance
+ *
+ * This process will create the instance visibility object containing private
+ * and protected members. The class instance is part of the prototype chain.
+ * This will be passed to all methods when invoked, permitting them to access
+ * the private and protected members while keeping them encapsulated.
+ *
+ * @param  {number}  iid       instance id
+ * @param  {Object}  instance  instance to initialize
+ *
+ * @return  {undefined}
+ */
+function initInstance( iid, instance )
+{
+    var prot = function() {};
+    prot.prototype = instance;
+
+    // add the visibility objects to the data object for this class instance
+    class_instance[ iid ] = new prot();
+}
+
+
 /**
  * Attaches __initProps() method to the class prototype
  *
@@ -469,14 +508,20 @@ function setupProps( func, abstract_methods, class_id )
  * @param  {Object}  prototype   prototype to attach method to
  * @param  {Object}  properties  properties to initialize
  *
+ * @param  {{public: Object, protected: Object, private: Object}}  members
+ *
  * @return  {undefined}
  */
-function attachPropInit( prototype, properties )
+function attachPropInit( prototype, properties, members )
 {
-    var prop_pub = properties[ 'public' ];
+    var prop_pub  = properties[ 'public' ],
+        prop_prot = properties[ 'protected' ]
+    ;
 
     util.defineSecureProp( prototype, '__initProps', function()
     {
+        var inst_props = class_instance[ this.__iid ];
+
         // first initialize the parent's properties, so that ours will overwrite
         // them
         var parent_init = prototype.parent.__initProps;
@@ -493,6 +538,25 @@ function attachPropInit( prototype, properties )
             // not share references (and therefore, data)
             this[ prop ] = util.clone( prop_pub[ prop ] );
         }
+
+        var methods_protected = members[ 'protected' ],
+            hasOwn            = Array.prototype.hasOwnProperty
+        ;
+
+        // copy over the methods
+        for ( method_name in methods_protected )
+        {
+            if ( hasOwn.call( methods_protected, method_name ) )
+            {
+                inst_props[ method_name ] = methods_protected[ method_name ];
+            }
+        }
+
+        // initialize protected properties and store in instance data
+        for ( prop in prop_prot )
+        {
+            inst_props[ prop ] = util.clone( prop_prot[ prop ] );
+        }
     });
 }
 
@@ -586,6 +650,20 @@ function attachId( func, id )
 }
 
 
+/**
+ * Attaches an instance identifier to a class instance
+ *
+ * @param  {Object}  instance  class instance
+ * @param  {number}  iid       instance id
+ *
+ * @return  {undefined}
+ */
+function attachInstanceId( instance, iid )
+{
+    util.defineSecureProp( instance, '__iid', iid );
+}
+
+
 /**
  * Attaches partially applied isInstanceOf() method to class instance
  *
@@ -615,7 +693,7 @@ function attachInstanceOf( instance )
 function createMeta( func, parent_id )
 {
     var id          = func.__cid,
-        parent_meta = ( ( parent_id ) ? getMeta( parent_id) : undefined );
+        parent_meta = ( ( parent_id ) ? getMeta( parent_id ) : undefined );
 
     // copy the parent prototype's metadata if it exists (inherit metadata)
     if ( parent_meta )
@@ -649,3 +727,26 @@ function getMeta( id )
     return class_meta[ id ] || {};
 }
 
+
+/**
+ * Returns the instance object associated with the given method
+ *
+ * The instance object contains the protected and private members. This object
+ * can be passed as the context when calling a method in order to give that
+ * method access to those members.
+ *
+ * @param  {function()}  method  method to look up instance object for
+ *
+ * @return  {Object,null}  instance object if found, otherwise null
+ */
+function getMethodInstance( method )
+{
+    var iid  = method.__iid,
+        data = class_instance[ method.__iid ];
+
+    return ( iid && data )
+        ? data
+        : null
+    ;
+}
+
diff --git a/lib/member_builder.js b/lib/member_builder.js
index 8d22af9..e5fec21 100644
--- a/lib/member_builder.js
+++ b/lib/member_builder.js
@@ -59,10 +59,15 @@ exports.initMembers = function( mpublic, mprotected, mprivate )
  * @param  {*}       value  property value
  *
  * @param  {Object.<string,boolean>}  keywords  parsed keywords
+
+ * @param  {Object=}  instCallback  function to call in order to retrieve
+ *                                  object to bind 'this' keyword to
  *
  * @return  {undefined}
  */
-exports.buildMethod = function( members, meta, name, value, keywords, cmp )
+exports.buildMethod = function(
+    members, meta, name, value, keywords, instCallback
+)
 {
     var prev;
 
@@ -104,12 +109,18 @@ exports.buildMethod = function( members, meta, name, value, keywords, cmp )
     if ( prev )
     {
         // override the method
-        dest[ name ] = overrideMethod( prev, value );
+        dest[ name ] = overrideMethod( prev, value, instCallback );
+    }
+    else if ( keywords[ 'abstract' ] )
+    {
+        // we do not want to wrap abstract methods, since they are not callable
+        dest[ name ] = value;
     }
     else
     {
-        // we are not overriding the method, so simply copy it over
-        dest[ name ] = value;
+        // we are not overriding the method, so simply copy it over, wrapping it
+        // to ensure privileged calls will work properly
+        dest[ name ] = overrideMethod( value, null, instCallback );
     }
 };
 
@@ -270,24 +281,42 @@ function scanMembers( members, name, cmp )
  * @param  {function()}  super_method      method to override
  * @param  {function()}  new_method        method to override with
  *
+ * @param  {Object=}  instCallback  function to call in order to retrieve
+ *                                  object to bind 'this' keyword to
+ *
  * @return  {function()}  override method
  */
-function overrideMethod( super_method, new_method )
+function overrideMethod( super_method, new_method, instCallback )
 {
+    instCallback = instCallback || function() {};
+
     // return a function that permits referencing the super method via the
     // __super property
-    var override = function()
+    var override = null;
+
+    if ( new_method )
     {
-        var tmp = this.__super;
+        override = function()
+        {
+            // the _super property will contain the parent method
+            this.__super = super_method;
 
-        // assign _super temporarily for the method invocation so
-        // that the method can call the parent method
-        this.__super = super_method;
-        var retval   = new_method.apply( this, arguments );
-        this.__super = tmp;
+            var retval = new_method.apply(
+                ( instCallback( this ) || this ), arguments
+            );
 
-        return retval;
-    };
+            return retval;
+        };
+    }
+    else
+    {
+        override = function()
+        {
+            return super_method.apply(
+                ( instCallback( this ) || this ), arguments
+            );
+        };
+    }
 
     // This is a trick to work around the fact that we cannot set the length
     // property of a function. Instead, we define our own property - __length.
diff --git a/test/inc-member_builder-common.js b/test/inc-member_builder-common.js
index 9a61d19..5aca382 100644
--- a/test/inc-member_builder-common.js
+++ b/test/inc-member_builder-common.js
@@ -35,7 +35,7 @@ exports.buildMember = null;
 
 
 /**
- * Partially applied function to quickly build properties using common test data
+ * Quickly build properties using common test data
  */
 exports.buildMemberQuick = function( keywords, preserve_prior )
 {
@@ -66,16 +66,25 @@ exports.assertOnlyVisibility = function( vis, name, value, message )
     var check = [ 'public', 'protected', 'private' ],
         i     = check.length,
         visi  = '',
+        value,
         cmp;
 
     // forEach not used for pre-ES5 browser support
     while ( i-- )
     {
-        visi = check[ i ];
-        cmp  = ( visi === vis ) ? value : undefined;
+        visi  = check[ i ];
+        value = exports.members[ visi ][ name ];
+        cmp   = ( visi === vis ) ? value : undefined;
+
+        // are we comparing functions?
+        if ( cmp && exports.funcVal )
+        {
+            cmp   = exports.funcVal;
+            value = value();
+        }
 
         assert.deepEqual(
-            exports.members[ visi ][ name ],
+            value,
             cmp,
             message
         );
diff --git a/test/test-class-constructor.js b/test/test-class-constructor.js
index c39dcf9..2262570 100644
--- a/test/test-class-constructor.js
+++ b/test/test-class-constructor.js
@@ -29,22 +29,21 @@ var common = require( './common' ),
 // these two variables are declared outside of the class to ensure that they
 // will still be set even if the context of the constructor is wrong
 var construct_count   = 0,
-    construct_context = null;
+    construct_context = null,
+    construct_args    = null
 
 // create a basic test class
-var Foo = Class.extend(
-{
-    args: null,
-
-
-    __construct: function()
+    Foo = Class.extend(
     {
-        construct_count++;
-        construct_context = this;
+        __construct: function()
+        {
+            construct_count++;
+            construct_context = this;
+            construct_args    = arguments;
+        },
+    })
+;
 
-        this.args = arguments;
-    },
-});
 
 assert.ok(
     ( Foo.prototype.__construct instanceof Function ),
@@ -67,19 +66,19 @@ assert.equal(
 );
 
 assert.equal(
-    obj,
-    construct_context,
+    construct_context.__iid,
+    obj.__iid,
     "Constructor should be invoked within the context of the class instance"
 );
 
 assert.notEqual(
-    obj.args,
+    construct_args,
     null,
     "Constructor arguments should be passed to the constructor"
 );
 
 assert.equal(
-    obj.args.length,
+    construct_args.length,
     args.length,
     "All arguments should be passed to the constructor"
 );
@@ -88,7 +87,7 @@ assert.equal(
 for ( var i = 0, len = args.length; i < len; i++ )
 {
     assert.equal(
-        obj.args[ i ],
+        construct_args[ i ],
         args[ i ],
         "Arguments should be passed to the constructor: " + i
     );
@@ -112,16 +111,16 @@ assert.equal(
 );
 
 assert.equal(
-    construct_context,
-    subobj,
+    construct_context.__iid,
+    subobj.__iid,
     "Parent constructor is run in context of the subtype"
 );
 
 // this should be implied by the previous test, but let's add it for some peace
 // of mind
 assert.ok(
-    ( ( subobj.args[ 0 ] === args2[ 0 ] )
-        && ( subobj.args[ 1 ] == args2[ 1 ] )
+    ( ( construct_args[ 0 ] === args2[ 0 ] )
+        && ( construct_args[ 1 ] == args2[ 1 ] )
     ),
     "Parent constructor sets values on subtype"
 );
@@ -135,14 +134,14 @@ assert.ok(
 );
 
 assert.equal(
-    construct_context,
-    subobj2,
+    construct_context.__iid,
+    subobj2.__iid,
     "Self-invoking constructor is run in the context of the new object"
 );
 
 assert.ok(
-    ( ( subobj2.args[ 0 ] === args2[ 0 ] )
-        && ( subobj2.args[ 1 ] == args2[ 1 ] )
+    ( ( construct_args[ 0 ] === args2[ 0 ] )
+        && ( construct_args[ 1 ] == args2[ 1 ] )
     ),
     "Self-invoking constructor receives arguments"
 );
diff --git a/test/test-class-visibility.js b/test/test-class-visibility.js
index 6f2647f..ad8a18a 100644
--- a/test/test-class-visibility.js
+++ b/test/test-class-visibility.js
@@ -30,9 +30,9 @@ var common = require( './common' ),
     prot = 'bar',
     priv = 'baz',
 
-    pubf  = function() {},
-    protf = function() {},
-    privf = function() {},
+    pubf  = function() { return pub; },
+    protf = function() { return prot; },
+    privf = function() { return priv; },
 
     // new anonymous class instance
     foo = Class.extend( {
@@ -43,6 +43,13 @@ var common = require( './common' ),
         'public pubf':     pubf,
         'protected protf': protf,
         'private privf':   privf,
+
+        'public getProp': function( name )
+        {
+            // return property, allowing us to break encapsulation for
+            // protected/private properties (for testing purposes)
+            return this[ name ];
+        },
     })();
 
 
@@ -55,8 +62,8 @@ var common = require( './common' ),
     );
 
     assert.equal(
-        foo.pubf,
-        pubf,
+        foo.pubf(),
+        pub,
         "Public methods are accessible via public interface"
     );
 } )();
@@ -89,3 +96,24 @@ var common = require( './common' ),
     );
 } )();
 
+
+/**
+ * Protected members should be accessible from within class methods
+ */
+( function testProtectedMembersAreAccessibleInternally()
+{
+    assert.equal(
+        foo.getProp( 'peeps' ),
+        prot,
+        "Protected properties are available internally"
+    );
+
+    // invoke rather than checking for equality, because the method may be
+    // wrapped
+    assert.equal(
+        foo.getProp( 'protf' )(),
+        prot,
+        "Protected methods are available internally"
+    );
+} )();
+
diff --git a/test/test-member_builder-method.js b/test/test-member_builder-method.js
index c5c711d..ab24e18 100644
--- a/test/test-member_builder-method.js
+++ b/test/test-member_builder-method.js
@@ -27,7 +27,8 @@ var common    = require( './common' ),
     mb_common = require( './inc-member_builder-common' )
 ;
 
-mb_common.value       = function() {};
+mb_common.funcVal     = 'foobar';
+mb_common.value       = function() { return mb_common.funcVal; };
 mb_common.buildMember = common.require( 'member_builder' ).buildMethod;
 
 // do assertions common to all member builders
@@ -50,7 +51,8 @@ mb_common.assertCommon();
  */
 ( function testCannotOverridePropertyWithMethod()
 {
-    mb_common.value = 'moofoo';
+    mb_common.value   = 'moofoo';
+    mb_common.funcVal = undefined;
     mb_common.buildMemberQuick();
 
     assert.throws( function()
@@ -151,3 +153,74 @@ mb_common.assertCommon();
     }, TypeError, "Cannot override concrete method with abstract method" );
 } )();
 
+
+/**
+ * One of the powerful features of the method builder is the ability to pass in
+ * an instance to be bound to 'this' when invoking a method. This has some
+ * important consequences, such as the ability to implement protected/private
+ * members.
+ */
+( function testMethodInvocationBindsThisToPassedInstance()
+{
+    var instance = function() {},
+        val      = 'fooboo',
+        val2     = 'fooboo2',
+        iid      = 1,
+
+        func = function()
+        {
+            return this.foo;
+        },
+
+        func2 = function()
+        {
+            return this.foo2;
+        },
+
+        called       = false,
+        instCallback = function()
+        {
+            called = true;
+            return instance;
+        },
+
+        members = { 'public': {}, 'protected': {}, 'private': {} }
+    ;
+
+    // set instance values
+    instance.foo  = val;
+    instance.foo2 = val2;
+
+    // concrete method
+    mb_common.buildMember(
+        members,
+        exports.meta,
+        'func',
+        func,
+        [ 'public' ],
+        instCallback
+    );
+
+    assert.equal(
+        members[ 'public' ].func(),
+        val,
+        "Calling method will bind 'this' to passed instance"
+    );
+
+    // override method
+    mb_common.buildMember(
+        members,
+        exports.meta,
+        'func',
+        func2,
+        [ 'public' ],
+        instCallback
+    );
+
+    assert.equal(
+        members[ 'public' ].func(),
+        val2,
+        "Calling method override will bind 'this' to passed instance"
+    );
+} )();
+