JBoss AS is a J2EE 1.4-certified, open source Java application server. It is the most widely used application server on the market. The highly flexible and easy-to-use server architecture has made JBoss AS the ideal choice for users just starting out with J2EE, as well as senior architects looking for a customizable middleware platform. The ready availability of the source code allows you to debug the server, learn its inner workings and create customized versions for your personal or business use. This guide will show you how to install JBoss AS 4.0. You will learn how to start and stop your JBoss instance, and you will also learn about the directory structure and understand what the key services and configuration files are.