How do I detect what .NET Framework versions and service packs are installed?

There is an official Microsoft answer to this question at the following knowledge base article:

Article ID: 318785 - Last Review: November 7, 2008 - Revision: 20.1 How to determine which versions of the .NET Framework are installed and whether service packs have been applied

Unfortunately, it doesn't appear to work, because the mscorlib.dll version in the 2.0 directory has a 2.0 version, and there is no mscorlib.dll version in either the 3.0 or 3.5 directories even though 3.5 SP1 is installed ... why would the official Microsoft answer be so misinformed?

The Framework 4 beta installs to a differing registry key.

using System;
using System.Collections.ObjectModel;
using Microsoft.Win32;

class Program
{
    static void Main(string[] args)
    {
        foreach(Version ver in InstalledDotNetVersions())
            Console.WriteLine(ver);

        Console.ReadKey();
    }


    public static Collection<Version> InstalledDotNetVersions()
    {
        Collection<Version> versions = new Collection<Version>();
        RegistryKey NDPKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP");
        if (NDPKey != null)
        {
            string[] subkeys = NDPKey.GetSubKeyNames();
            foreach (string subkey in subkeys)
            {
                GetDotNetVersion(NDPKey.OpenSubKey(subkey), subkey, versions);
                GetDotNetVersion(NDPKey.OpenSubKey(subkey).OpenSubKey("Client"), subkey, versions);
                GetDotNetVersion(NDPKey.OpenSubKey(subkey).OpenSubKey("Full"), subkey, versions);
            }
        }
        return versions;
    }

    private static void GetDotNetVersion(RegistryKey parentKey, string subVersionName, Collection<Version> versions)
    {
        if (parentKey != null)
        {
            string installed = Convert.ToString(parentKey.GetValue("Install"));
            if (installed == "1")
            {
                string version = Convert.ToString(parentKey.GetValue("Version"));
                if (string.IsNullOrEmpty(version))
                {
                    if (subVersionName.StartsWith("v"))
                        version = subVersionName.Substring(1);
                    else
                        version = subVersionName;
                }

                Version ver = new Version(version);

                if (!versions.Contains(ver))
                    versions.Add(ver);
            }
        }
    }
}

Enumerate the subkeys of HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP. Each subkey is a .NET version. It should have Install=1 value if it's present on the machine, an SP value that shows the service pack and an MSI=1 value if it was installed using an MSI. (.NET 2.0 on Windows Vista doesn't have the last one for example, as it is part of the OS.)

For a 64-bit OS, the path would be:

HKEY_LOCAL_MACHINE\SOFTWARE\wow6432Node\Microsoft\NET Framework Setup\NDP\

Update for .NET 4.5.1

Now that .NET 4.5.1 is available the actual value of the key named Release in the registry needs to be checked, not just its existence. A value of 378758 means that .NET Framework 4.5.1 is installed. However, as described here this value is 378675 on Windows 8.1.

There is a GUI tool available, ASoft .NET Version Detector, which has always proven highly reliable. It can create XML files by specifying the file name of the XML output on the command line.

You could use this for automation. It is a tiny program, written in a non-.NET dependent language and does not require installation.

I was needing to find out just which version of .NET framework I had on my computer, and all I did was go to the control panel and select the "Uninstall a Program" option. After that, I sorted the programs by name, and found Microsoft .NET Framework 4 Client Profile.

Here is a PowerShell script to obtain installed .NET framework versions

function Get-KeyPropertyValue($key, $property)
{
    if($key.Property -contains $property)
    {
        Get-ItemProperty $key.PSPath -name $property | select -expand $property
    }
}

function Get-VersionName($key)
{
   $name = Get-KeyPropertyValue $key Version
   $sp = Get-KeyPropertyValue $key SP
   $install = Get-KeyPropertyValue $key Install
   if($sp)
   {
        "$($_.PSChildName) $name SP $sp"
   }
   else{
    "$($_.PSChildName) $name"
   }
}

function Get-FrameworkVersion{
   dir "hklm:\SOFTWARE\Microsoft\NET Framework Setup\NDP\" |? {$_.PSChildName -like "v*"} |%{
    if( $_.Property -contains "Version")
    {
        Get-VersionName $_
    }
    else{
        $parent = $_
        Get-ChildItem $_.PSPath |%{
            $versionName = Get-VersionName $_
            "$($parent.PSChildName) $versionName"
            }
        }
    }
}


$v4Directory = "hklm:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full"
if(Test-Path $v4Directory)
{
    $v4 = Get-Item $v4Directory
    $version = Get-KeyPropertyValue $v4 Release
    switch($version){
        378389 {".NET Framework 4.5"; break;}
        378675 {".NET Framework 4.5.1 installed with Windows 8.1 or Windows Server 2012 R2"; break;}
        378758 {".NET Framework 4.5.1 installed on Windows 8, Windows 7 SP1, or Windows Vista SP2"; break;}
        379893 {".NET Framework 4.5.2"; break;}
        { 393295, 393297 -contains $_} {".NET Framework 4.6"; break;}
        { 394254, 394271 -contains $_} {".NET Framework 4.6.1"; break;}
        { 394802, 394806 -contains $_} {".NET Framework 4.6.2"; break; }
    }
}

It was written based on How to: Determine Which .NET Framework Versions Are Installed. Please use THE Get-FrameworkVersion() function to get information about installed .NET framework versions.

Using the Signum.Utilities library from SignumFramework (which you can use stand-alone), you can get it nicely and without dealing with the registry by yourself:

AboutTools.FrameworkVersions().ToConsole();
//Writes in my machine:
//v2.0.50727 SP2
//v3.0 SP2
//v3.5 SP1

See How to: Determine Which .NET Framework Versions Are Installed (MSDN).

MSDN proposes one function example that seems to do the job for version 1-4. According to the article, the method output is:

v2.0.50727  2.0.50727.4016  SP2
v3.0  3.0.30729.4037  SP2
v3.5  3.5.30729.01  SP1
v4
  Client  4.0.30319
  Full  4.0.30319

Note that for "versions 4.5 and later" there is another function.

In Windows 7 (it should work for Windows 8 also, but I haven't tested it):

Go to a command prompt

Steps to go to a command prompt:

1. Click Start Menu
2. In Search Box, type "cmd" (without quotes)
3. Open cmd.exe

In cmd, type this command

wmic /namespace:\\root\cimv2 path win32_product where "name like '%%.NET%%'" get version

This gives the latest version of NET Framework installed.

One can also try Raymond.cc Utilties for the same.