Internet technology continues to grow fast and has now become the dominant computing technology in developing software and computing applications. By fully taking advantage of the quick development of the service concept and modeling, Web services technology, as part of Internet technology, has rapidly evolved and made a drastic impact on enterprise integration. A deployed Web based service, relying on a suite of Internet based standard protocols, is self-contained, self-describing, and network-neutral computing component. It can be readily deployed, published, located, and invoked over the heterogeneous networks. This chapter starts with a brief introduction to the concepts of services and enterprise service computing. The Web service’s technical fundamentals are then fully explored. XML, SOAP, WSDL, and UDDI as the core technologies are further explained in great detail. Implementation examples are finally used to demonstrate how the Web services technology can be typically applied in integrating distributed applications across an organization.