STATEMATE is a set of tools, with a heavy graphical orientation, intended for the specification, analysis, design, and documentation of large and complex reactive systems. It enables a user to prepare, analyze, and debug diagrammatic, yet precise, descriptions of the system under development from three interrelated points of view, capturing structure, functionality, and behavior. These views are represented by three graphical languages, the most intricate of which is the language of statecharts, used to depict reactive behavior over time. In addition to the use of statecharts, the main novelty of STATEMATE is in the fact that it understands the entire descriptions perfectly, to the point of being able to analyze them for crucial dynamic properties, to carry out rigorous executions and simulations of the described system, and to create running code automatically. These features are invaluable when it comes to the quality and reliability of the final outcome.>