The Enterprise JavaBeans architecture or EJB for short is an architecture for the development and deployment of component-based robust, highly scalable business applications. These Applications are scalable, transactional, and multi-user secure. You can develop the application once and then deploy on any one of the Java EE 5 compliant application server. There are many application servers available, both free and commercial. You can choose the server for development and deployment to suit your requirement and budget.
Benefits of EJB
EJB simplifies the development of small and large enterprise applications. The EJB container provides system-level services to enterprise beans, the bean developer can just concentrate on developing logic to solve business problems.
see in wiki for more detail to getting stated
