When compiling a .NET application you often use the command line tools csc or vbc to compile the code to a dll file. However, the path environment variable does not always contain it (if all you have done is install the framework, or use SharpDevelop ). Here is a way to add the folder to the path via a batch file. It does not add it twice if you have already added it to the path (i.e. it checks the path before adding). Don't run directly, rather place it somewhere that is already in the path (e.g. c:\windows\system32), and do Start > Run > cmd /k DotNetSetPath[1.0|1.1|2.0] "DotNetSetPath 1.0" for v1.0 of the framework, "DotNetSetPath 1.1" for v1.1, "DotNetSetPath 2.0" or "DotNetSetPath" for v2.0 Update (13 Feb, 2006) : .NET 2.0 is now an option DotNetSetPath.cmd @echo off rem v1.0.3705 is .NET 1.0, v1.1.4322 is .NET 1.1, v2.0.50727 is .NET 2.0 if "%1"=="2.0" goto dotnet20 if "%1"=="1.1"...