From the authors
“jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers. With a combination of versatility and extensibility, jQuery has changed the way that millions of people write JavaScript.”
Our one-paragraph review
jQuery is an absolute requirement for any browser-based application or site. Why write 100 lines of DOM manipulation code using the W3C API when you can do the same work in 3 lines of jQuery? Plus, there are hundreds if not thousands of jQuery-based plugins available, many either free or modestly priced. These plugins solve common problems so that you don't have to.