C# - How To Maintain State Between Pages

I am working on an existing project, setup by another coder. I'm having some trouble understanding how state is being maintained between pages. There is a Class library which has some helper objects. Mostly these objects are just used for there static methods and rarely instantiated or inherited.

This is an example class I'm testing with.

public sealed class Application
{
public static string Test;
}

Now when i run something like the following in the base class of my page, I would expect the result to be "1: 2:Test" all the time (note that "1" is empty), but strangly its only this way the first time it is run. Then every time afterwards its "1:Test 2:Test". Somehow its maintaining the state of the static variable between pages and being refreshed??

Response.Write("1:" + SharedLibrary.Application.Test);
SharedLibrary.Application.Test = "Test";
Response.Write(" 2:" + SharedLibrary.Application.Test);

I need to create more classes like this, but want to understand why this is occurring in the first place.