Getting the .NET Framework directory path

The path to the installation directory of the CLR active for the current .NET application can be obtained by using the following method:

System.Runtime.InteropServices.RuntimeEnvironment.GetRuntimeDirectory()

I would strongly advice against reading the registry directly. For example, when a .NET application is running in 64bit systems, the CLR can either be loaded from "C:\Windows\Microsoft.NET\Framework64\v2.0.50727" (AnyCPU, x64 compilation targets) or from "C:\Windows\Microsoft.NET\Framework\v2.0.50727" (x86 compilation target). Reading registry will not tell you which one of the two directories was used by the current CLR.

Another important fact is that "the current CLR" will be "2.0" for .NET 2.0, .NET 3.0 and .NET 3.5 applications. This means that the GetRuntimeDirectory() call will return 2.0 directory even within .NET 3.5 applications (that load some of their assemblies from 3.5 directory). Depending on your interpretation of the term ".NET Framework directory path", GetRuntimeDirectory might not be the information you are looking for ("CLR directory" versus "directory from which 3.5 assemblies are coming from").

An easier way is to include the Microsoft.Build.Utilities assembly and use

using Microsoft.Build.Utilities;
ToolLocationHelper.GetPathToDotNetFramework(
        TargetDotNetFrameworkVersion.VersionLatest);