Web services are the medium by which ArcGIS for Server communicates. They are the cogs that drive Server and feed your end users. ArcGIS for Server supports many types of web services. Each of these types implement an international standard, which is supported by various clients. Before we go through these standards or protocols, we will first define what a web service is. Then, you will create your first web service using the classic Active Server Pages (ASP). This exercise will cement the idea of web services and will let you further understand how they work. It will also prepare you for the second part of this chapter where you will learn how to author web services specifically for Server. The services that you will be publishing on Server are a little different from the classical web services. They have a geographic flavor to it. This is why throughout this chapter, we will refer to web services published on Server as GIS services.