Contexts and Dependency Injection (CDI) defines a set of complementary services that help improve the structure of application code.

• A well-defined lifecycle for stateful {@linkplain javax.enterprise.inject beans} bound to well-defined lifecycle {@linkplain javax.enterprise.context contexts}, where the set of contexts is {@linkplain javax.enterprise.context.spi extensible}
• A sophisticated, typesafe {@linkplain javax.enterprise.inject dependency injection mechanism}, including the ability to select dependencies at either {@linkplain javax.inject.Qualifier development} or {@linkplain javax.enterprise.inject.Alternative deployment} time, without verbose configuration
• Support for Java EE modularity and the Java EE component architecture—the modular structure of a Java EE application is taken into account when resolving dependencies between Java EE components
• {@linkplain javax.enterprise.inject Integration} with the Unified Expression Language, allowing any bean to be used directly within a JSF or JSP page
• The ability to {@linkplain javax.decorator decorate} injected beans
• The ability to associate {@linkplain javax.interceptor interceptors} with beans via typesafe {@linkplain javax.enterprise.inject interceptor bindings}
• An {@linkplain javax.enterprise.event event} notification model
• A web {@linkplain javax.enterprise.context.ConversationScoped conversation context} in addition to the three standard web contexts defined by the Java Servlets specification
• An {@linkplain javax.enterprise.inject.spi SPI} allowing portable extensions to integrate cleanly with the container

CDI allows objects to be bound to lifecycle contexts, to be injected, to be associated with interceptors and decorators, and to interact in a loosely coupled fashion by {@linkplain javax.enterprise.event.Event firing} and {@linkplain javax.enterprise.event.Observes observing} events. {@linkplain javax.enterprise.inject Various kinds} of objects are injectable, including EJB 3 session beans, managed beans, {@linkplain javax.enterprise.inject.Produces producer methods} and Java EE resources. We refer to these objects in general terms as beans and to instances of beans that are bound to contexts as contextual instances.