The main botteneck for using new applications is provided at the interface level, interactive computing strongly relies on a correct understanding of the computation state as shown on the screen, typically with visual structures such as icons, state diagrams, widgets of different sorts. The emphasis is on communication with a variety of user models so that no ambiguity may arise and that the effort insumed is proportional to the difficulty of the task. A number of visual interfaces and environments will be described as well as some evaluation metrics essentially based on usability criteria.