What is Swing?

Swing is part of the Java Foundation Classes (http://java.sun.com/products/jfc/) that defines a second generation of Graphical User Interface (GUI) components for Java. They provide a richer set of components over the original Abstract Window Toolkit (AWT) components originally provided with Java. First introduced to work as an extension to the Java 1.1 platform, they became a standard part of Java with the Java 2, version 1.2 release.

Sandip Chitale adds

Also see The Swing Connection at http://java.sun.com/products/jfc/tsc

Simon Brown adds

If you are considering using Swing for developing user interfaces, I can also recommend the Java Look and Feel Guidelines (http://java.sun.com/products/jlf/guidelines.html) to help you ensure consistency and ease of use in your end product.