The term web service implies “something” accessible on the “web” that gives you a “service.” The first example that comes to our mind is an HTML page: it’s accessible online and, once read, it gives you the information you were looking for. Another kind of web service is the Servlets. They are bound to a URL, therefore accessible on the web, and they perform any kind of processing. But the term “web services” quickly became a buzzword, got assimilated to Service Oriented Architecture (SOA) and today web services are part of our day-to-day architectural life. Web services applications can be implemented with different technologies such as SOAP, described in this chapter, or REST (see next chapter).