User Software Engineering is a methodology for the specification and implementation of interactive information systems. An early step in the methodology is the creation of a formal executable description of the user interaction with the system, based on augmented state transition diagrams. This paper shows the derivation of the USE transition diagrams based on perceived shortcomings of the "pure" state transition diagram approach. In this way, the features of the USE specification notation are gradually presented and illustrated. The paper shows both the graphical notation and the textual equivalent of the notation, and briefly describes the automated tools that support direct execution of the specification.