The two are similar at first glance but pretty different when you get into it. jQuery specializes in making javascript/DOM interaction drop dead simple. Nothi

The two are similar at first glance but pretty different when you get into it. jQuery specializes in making javascript/DOM interaction drop dead simple. Nothing else out there comes close to achieving this as well as jQuery. When I write with jQuery, the most basic pages are written functionally and when I need something more advanced it's easy to step into some OO. But, jQuery does nothing to help with object oriented javascript, you have to use javascripts prototype model. MooTools specializes in being more of a javascript framework. It adds functionality to javascript (which is controversial in itself), and lends itself to a very classical object oriented development approach. Both tools are quality, jQuery has a huge user base, whereas MooTools has a smaller and very rabid user base. If your project is a very UI/javascript focused project then MooTools may be the right answer. If it is not, and is just your typical site/application, then jQuery is probably it.