Simple Object Access Protocol (SOAP) is a way to create widely distributed, complex computing environments that run over the Internet using existing Internet infrastructure. SOAP is about applications communicating directly with each other over the Internet in a very effective way.

SOAP is an XML-based messaging protocol. It defines a set of rules for structuring messages that can be used for simple one-way messaging but is particularly useful for performing Remote Procedure Call (RPC)-style request-response dialogues. Messages are routed along the message-path, irrespective of the protocol to which SOAP is bound. This allows processing messages at one or more intermediate nodes in addition to the ultimate destination.

An advantage of SOAP is that program calls are much more likely to get through fire wall servers that screen out requests other than those for known applications (through the designated port mechanism). HTTP requests are usually allowed through fire walls. Hence, the applications can communicate with other applications using SOAP over HTTP.

SOAP enables message exchange over a variety of underlying protocols. As the SOAP messaging framework is independent of the underlying protocol, each intermediary can choose to use a different communication protocol without affecting the SOAP message. However, standard protocol bindings are necessary to ensure high levels of interoperability across SOAP applications and infrastructure. A concrete protocol binding defines exactly how SOAP messages must be transmitted with a given protocol.

A Service Container processes these request or response SOAP messages according to the formal set of conventions defined by SOAP. It is responsible for enforcing the rules that govern the exchange of SOAP messages and accesses the services provided by the underlying protocols through SOAP bindings.