Software engineers use system visualization mainly in two domains: algorithm visualization and system visualization, and both of these are often animated. In this paper we provide a generic link between the specification and animation of complex object-oriented reactive systems, which constitute one of the most important and difficult classes of systems. The link and its methodology form a basis for communication between standard reactive specification tools and standard animation tools. Reactive Animation can be used in a wide range of applications: computer games, navigation and traffic systems, interactive scientific visualization. Reactive Animation helps make the programming of such applications more reliable, expeditious and natural to observe and comprehend. We illustrate two examples: a complex biological model of thymic T-cell behavior and a traffic simulation(1).