Clearly, once you are comfortable with your .NET programming language of choice, your next goal as a .NET developer is to get to know the wealth of types defined in the (numerous) .NET namespaces. The most fundamental namespace to get your head around initially is named System. This namespace provides a core body of types that you will need to leverage time and again as a .NET developer. In fact, you cannot build any sort of functional C# application without at least making a reference to the System namespace, as the core data types (e.g., System.Int32, System.String) are defined here. Table offers a rundown of some (but certainly not all) of the .NET namespaces grouped by related functionality.