Hi, Here's a simple example of how Delphi 3.0 implements interfaces. The main difference between this and what Frank was suggesting is that Delphi 3.0 doesn't allow and fields in an interface. This is because COM is designed to work across process and machine boundaries using remote procedure calls(RPC) but does have support for remote variable calls(if there is such a thing!) and this is the main reason for using interfaces... this simple example of a Delphi interface is from a copy of a unit I'm working on to use MS ActiveScripting. the interface bit: const SIID_IActiveScriptSiteWindow = '{D10F6761-83E9-11cf-8F20-00805F2CD064}'; type IActiveScriptSiteWindow = interface(IUnknown) [SIID_IActiveScriptSiteWindow] function GetWindow( out phwnd : HWND ):HResult; stdcall; function EnableModeless( fEnable : boolean ):HResult; stdcall; end; a class that implements that interface: THostSite = class(TInterfacedObject, IActiveScriptSite, IActiveScriptSiteW indow) public Shell : THostShell; constructor Create( pshell : THostShell ); destructor Destroy; override; <code snipped> {** IActiveScriptSiteWindow **} function GetWindow( out phwnd : HWND ):HResult; stdcall; function EnableModeless( fEnable : boolean ):HResult; stdcall; end; The TInterfacedObject is the base object for the class and the IActiveScriptSite and IActiveScriptSiteWindow are interfaces it supports. You access an interface using the QueryInterface function in the IUnknown interface from which all interfaces are derived by passing it the interfaces IID. Hope this is of some interest. Sorry about the formatting of the code...I foolishly installed a beta of MS Outlook Express which doesn't like to put spaces at the start of a line occasionally.... Dave Dave Fiddes, CALM Software Production Officer Department of Mathematics, Heriot-Watt University, Edinburgh email D.J.Fiddes@hw.ac.uk - Tel: 0131-451-3251