One of the main goals of the HP Interactive Visual Interface (HP IVI) project was to leverage features from current user interface and software design technologies and blend the best of each into the feature set and design of the application program interface (API) functions. In doing so, the project team investigated windowing, graphics, the X toolkit (Xt Intrinsics), widgets, and object-oriented design. This article discusses the features used from each of these technologies, and how these features are incorporated into the internal design and implementation of the API functions.