Application integration can be made simpler, quicker and cheaper using a Service-Oriented Architecture (SOA).
Applications are exposed to one another as services using standard reusable interfaces.
An Enterprise Service Bus (ESB) is a general architectural pattern that provides the infrastructure needed to integrate these services flexibly and quickly. This pattern can be implemented using a variety of middleware technologies and programming models. The value of an ESB is that you can use it in a variety of scenarios - from departmental to enterprise-wide integration.
System downtime can be reduced, and changing business needs met, by dynamically adding or replacing services. Services can be plugged into the bus, and integrated with existing services, without the need to change existing services.