As with any IDL (Interface Definition Language) which plays the role of service describer in CORBA, WSDL is an XML syntax used to describe Web Services. Its specifications are the result of a joint effort from Microsoft, IBM and Ariba.

Microsoft already has a SOAP service description language called SDL (Service Definition Language). SDL, although present in November's SOAPToolkit version, is replaced by WSDL (Web Service Definition Language) in the new version, Toolkit 2.0 Beta 1, as Microsoft is currently repositioning itself.

The same three companies (Microsoft, IBM and Ariba) are also behind another initiative called UDDI (Universal Description, Discovery and Integration), whose aim is to form a series of directories which will reference companies offering B2B oriented services and, more specifically, Web Services. The first implementation of the Business Registry UDDI project was launched in November 2000 with the participation of Ariba, IBM and Microsoft, all three of whom are operating a distributed UDDI base (UDDI Registry). Although launched outside of the UDDI group, the WSDL specification should quickly find its niche within UDDI as a standard for describing Web Services.

The WSDL specification is available on IBM's developerWorks site and on Microsoft's site. WSDL is an important factor in the development of SOAP, and it facilitates the interoperability of Web Services. An increasing number of SOAP implementations support this description language. Thanks to WSDL, SOAP implementations can self-configure exchanges between Web Services while masking most of the technical details.