I have a need coming up to write a small c# WPF application. Some of the processes it does will need to be called by an ASP.Net application.
My question is how do I setup something that the web application can call and set the wpf application to work?
OR should I create a separate class library that performs processes and reference this in both applications?
Yes; you should create a separate class library.
The class library should not reference WPF or ASP.Net assemblies.