Enterprise JavaBeans currently offers four component types: stateful session beans, stateless session beans, bean-managed persistence entity beans and container-managed persistence entity beans.
These four types of EJBs clearly reflect the common needs of typical software applications.
JavaBeans is a key part in the Java 2 Enterprise Edition (J2EE), which specifies a larger component infrastructure that defines interaction between EJB and other component models such as Java Servlets.
With EJBs you can engineer from the simplest software to the largest enterprise applications.