AppDomains are usually created by hosts. Examples of hosts are the Windows Shell, ASP.NET and IE. When you run a .NET application from the command-line, the host is the Shell. The Shell creates a new AppDomain for every application.
AppDomains can also be explicitly created by .NET applications. Here is a C# sample which creates an AppDomain, creates an instance of an object inside it, and then executes one of the object’s methods:

using System;
using System.Runtime.Remoting;
using System.Reflection;
public class CAppDomainInfo : MarshalByRefObject
{
public string GetName() { return AppDomain.CurrentDomain.FriendlyName; }
}
public class App
{
public static int Main()
{
AppDomain ad = AppDomain.CreateDomain( “Andy’s new domain” );
CAppDomainInfo adInfo = (CAppDomainInfo)ad.CreateInstanceAndUnwrap(
Assembly.GetCallingAssembly().GetName().Name, “CAppDomainInfo” );
Console.WriteLine( “Created AppDomain name = ” + adInfo.GetName() );
return 0;
}
}