C# Definition:

[ComImport]
[Guid("6d5140c1-7436-11ce-8034-00aa006009fa")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IServiceProvider {
    void QueryService(ref Guid guidService, ref Guid riid,
        [MarshalAs(UnmanagedType.Interface)] out object ppvObject);
    }

VB Definition:

<ComImport(),
Guid("6d5140c1-7436-11ce-8034-00aa006009fa"),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _
Interface IServiceProvider
    Sub QueryService(ByRef guidService As Guid, ByRef riid As Guid,
    <MarshalAs(UnmanagedType.Interface)> ByRef ppvObject As Object)
End Interface

User-Defined Types:

None.

Notes:

The IServiceProvider defined here is different with "System.IServiceProvider". To remove name collisition, rename "IServiceProvider" to other name such as "UCOMIServiceProvider". Otherwise, you should use fully qualified namespace to the interface since you will normally use "using System" directive.

The QueryService above does not work for me: ppvObject is always marshalled as IUnknown, as documented in the .Net API docs. I use the following:

    [ComImport]
    [Guid("6d5140c1-7436-11ce-8034-00aa006009fa")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IServiceProvider {
    void QueryService(ref Guid guidService, ref Guid riid,
              out IntPtr ppvObject);
    }

I then assign to ppvObject using:

    ppvObject = Marshal.GetComInterfaceForObject(objectWithRequiredInterface,
            typeof(IRequiredInterface));