Essential .NET, Volume 1: The Common Language Runtime

Execution Scope and the CLR

AppDomains fill many of the same roles filled by an operating system process. AppDomains, like processes, scope the execution of code. AppDomains, like processes, provide a degree of fault isolation. AppDomains, like processes, provide a degree of security isolation. AppDomains, like processes, own resources on behalf of the programs they execute. In general, most of what you may know about an operating system process probably applies to AppDomains.

AppDomains are strikingly similar to processes, but they are ultimately two different things. A process is an abstraction created by your operating system. An AppDomain is an abstraction created by the CLR. Whereas a given AppDomain resides in exactly one OS process, a ...