It is a "lightweight protocol for exchange of information in a decentralized, distributed environment" [1] XML based messaging Support for message routing Encoding rules for expressing data types (XML Schema) Conventions for using SOAP for RPC Transport Independence WSDL, UDDI, MIME and DIME attachements, SOAP Authentication, ebXML, XML Security, etc. [1] from the SOAP specs, http://www.w3.org/TR/SOAP/