Ran across some interesting information in my research. This should be apparent to anyone who has created secondary AppDomains in .NET before, but for me my current work is the first time that I have had a need to implement this very cool feature of the CLR. Once you create an application domain and call a method in it, the method call is occurring on the current thread in a synchronous manner. The thread simply switches context between the default appdomain and your secondary appdomain. In my case, I have a scheduling application where I wanted to isolate the effects of the process, but also needed it to be multi-threaded. Thus the use of AppDomain, and also the auxillary use of threads to increase throughput for the scheduler.