After a maturing process where models and architectures for User Interface Systems have been dened and generally accepted, the current expectations of researchers, developers and users, are centered around user interface (UI) construction tools incorporating rapid prototyping facilities. This paper describes the approach taken in the design and implementation of a system for interactive UI construction. The INGRID system (INteractive GRaphical Interface Designer), is based on a comprehensive UI architecture, a run time support providing interactive programming facilities in C++, and a set of dedicated editors incorporating direct manipulation techniques. The object oriented approach is present, both in the design of the tool itself, and in the proposed methodology for user interface development.