Collins presents a principled approach to designing user interfaces for systems built on modern hardware and software platforms. In the text, Collins defines object-oriented user interface, presents a methodology for designing both the visible features of the interface and the software structures underlying it, and demonstrates how this methodology fits into the context of object-oriented development. Collins provides the reader with a single conceptual model, grounded in standard engineering practice, to guide both external and internal design of the user interface. The author's methodology, based on object-oriented principles, is consistent with other object-oriented methodologies for system and database design.