SOAP: Simple Object Access Protocol (SOAP) standard an XML language defining a message architecture and message formats, is used by Web services it contain a description of the operations. WSDL is an XML-based language for describing Web services and how to access them. will run on SMTP,HTTP,FTP etc. Requires middle-ware support, well defined mechanism to define services like WSDL+XSD, WS-Policy SOAP will return XML based data.
REST: Representational State Transfer (RESTful) web services. they are second generation Web Services. RESTful web services, communicate via HTTP than SOAP-based services and do not require XML messages or WSDL service-API definitions. For REST, no middle-ware is required only HTTP support is needed. WADL Standard, REST can return XML, plain text, JSON, HTML etc