1.) DoSomethingLocal is defined as $.fn.DoSomethingLocal. You can add as many custom functions to the jQuery.fn (or simply $.fn) object as required by your plugin implementation. Any function you add to the $.fn object is assumed to work on references to an instance of an element/object that was selected. This is what the $.fn Syntax means - we are simply adding a custom interface to a jQuery object that assumes selected elements. 2.) DoSomethingGlobal is applied directly to the global jQuery object as $.DoSomethingGlobal. A function attached to the jQuery framework in such way assumes that it will not work on selected elements but rather it will work in the global scope and contain practically any implementation.