Service Oriented Infrastructures (SOIs) have recently seen increased use, mainly thanks to technologies for data centre virtualization and the emergence and increasing commercial offering of Cloud solutions. Web Services have been seen as a tool to implement SOI solutions thanks to their versatility and interoperability, but at the same time, Web Services have been considered not suitable for providing interactive real-time solutions. In this chapter the state of the art of the Web service technology will be analysed, and their different communication mechanisms and the existing implementations will be compared. Firstly, the different standardisation bodies working on Web service specifications relevant to SOI will be introduced. The various approaches to implement Web services will be described followed by the Web service specifications and the middleware that make use of those specifications, including the description of the commercial interfaces and development tools to create services for the cloud. In the last part of the chapter, the interoperability problems present on the different frameworks and the existing solutions to minimize those interoperability problems will be explained.