C# Signature:

[DllImport("shell32.dll")]
static extern int SHGetKnownFolderPath(
    [MarshalAs(UnmanagedType.LPStruct)] Guid rfid,
    uint dwFlags,
    IntPtr hToken,
    out IntPtr ppszPath); // must be freed with Marshal.FreeCoTaskMem

C# Signature with marshaling:

[DllImport("shell32.dll", CharSet = CharSet.Unicode, ExactSpelling = true, PreserveSig = false)]
static extern string SHGetKnownFolderPath(
    [MarshalAs(UnmanagedType.LPStruct)] Guid rfid,
    uint dwFlags,
    IntPtr hToken = default);

VB Signature:

<DllImport("shell32.dll")> _
Shared Function SHGetKnownFolderPath(
    <MarshalAs(UnmanagedType.LPStruct)> ByVal rfid As Guid,
    ByVal dwFlags As UInteger,
    ByVal hToken As IntPtr,
    ByRef ppszPath As IntPtr ' must be freed with Marshal.FreeCoTaskMem
    ) As Integer
End Function

VB Signature with marshaling:

<DllImport("shell32.dll", CharSet:=CharSet.Unicode, ExactSpelling:=True, PreserveSig:=False)>
Shared Function SHGetKnownFolderPath(
    <MarshalAs(UnmanagedType.LPStruct)> ByVal rfid As Guid,
    ByVal dwFlags As UInteger,
    ByVal hToken As IntPtr
    ) As String
End Function

User-Defined Types:

The list of values for the rfid Guid are available on KNOWNFOLDERID.

Alternative Managed API:

• The built-in System.Environment.GetFolderPath method. This method does not provide access to folders introduced since Windows Vista (like the Downloads folder): https://docs.microsoft.com/en-us/dotnet/api/system.environment.getfolderpath
• The Visual Basic .NET portability API My.Computer.FileSystem.SpecialDirectories. This method does not provide access to folders introduced since Windows Vista (like the Downloads folder): https://docs.microsoft.com/en-us/dotnet/api/microsoft.visualbasic.fileio.specialdirectories

Notes:

• If you do not use the marshaling version, you convert the returned ppszPath to a string with Marshal.PtrStringToUni. You must always call Marshal.FreeCoTaskMem on it afterwards, even if the method returns a failure code.
• If you use the marshaling version, which automatically throws exceptions if the method returns a failure code, the failure code to exception mapping is available here: https://docs.microsoft.com/en-us/dotnet/framework/interop/how-to-map-hresults-and-exceptions
• Not all folders are available on every system (for example, the playlists folder). Check the returned failure code or exception.
• This returns the internal / actual file system path. The folder name displayed in the File Explorer may be localized, e.g. the Playlists folder showing as "Musikwiedergabelisten" on a German system. To retrieve the localized name, instantiate an IShellItem with SHGetKnownFolderItem, and call its GetDisplayName method.

Sample Code (C#):

// C#
using System.Runtime.InteropServices;

public static string? GetKnownFolderPath(Guid folderGuid)
{
    IntPtr ppszPath = default;
    try
    {
        int hr = SHGetKnownFolderPath(folderGuid, 0, IntPtr.Zero, out ppszPath);
        Marshal.ThrowExceptionForHR(hr); // alternatively, check success with hr >= 0
        return Marshal.PtrToStringUni(ppszPath);
    }
    finally
    {
        Marshal.FreeCoTaskMem(ppszPath);
    }
}

Sample Code with marshaling (C#):

// C#
public static string GetKnownFolderPath(Guid folderGuid)
{
    return SHGetKnownFolderPath(folderGuid, 0);
}

Sample Code (VB.NET):

' VB.NET
Public Shared Function GetKnownFolderPath(ByVal folderGuid As Guid) As String
    Dim ppszPath As IntPtr
    Try
        Dim hr As Integer = SHGetKnownFolderPath(folderGuid, 0, IntPtr.Zero, ppszPath)
        Marshal.ThrowExceptionForHR(hr) ' alternatively, check success with hr >= 0
        Return Marshal.PtrToStringUni(ppszPath)
    Finally
        Marshal.FreeCoTaskMem(ppszPath)
    End Try
End Function

Sample Code with marshaling (VB.NET):

' VB.NET
Public Shared Function GetKnownFolderPath(ByVal folderGuid As Guid) As String
    Return SHGetKnownFolderPath(folderGuid, 0, IntPtr.Zero)
End Function