Enterprise JavaBeans is the server-side component architecture for the J2EE platform. EJB enables rapid and simplified development of distributed, transactional, secure and portable Java applications.
Since its introduction over four years ago, Enterprise JavaBeans (EJB) technology has gained unprecedented momentum among both platform providers and enterprise developers.
That's because the EJB component model simplifies the development of middleware applications by providing automatic support for services such as transactions, security, database connectivity, and more.
The EJB 2.1 specification enhances the EJB architecture with support for Web services. Enterprise developers can implement and deploy Web service applications with the same level of ease as other server-side applications.
In addition, EJB 2.1 provides a container-managed Timer Service; enhancements to EJB QL -- the declarative language for container-managed persistence -- to support aggregate and order-by operations; and a generalization of message-driven beans to support additional messaging types.
Source : Site de Sun