This paper describes some aspects of an interactive graphical tool designed to exhibit, through animation, the dynamic behaviour of parallel systems of communicating processes. The tool, called VisualNets, provides functionalities for visually creating graphical representations of processes, connecting them via channels, defining their behaviours in Hoare’s CSP notation and animating the evolution of their visulization with time. The tool is very useful for understanding concurrency, analysing various aspects of distributed message-passing algorithms, detecting deadlocks, identifying computational bottlenecks, and estimating the performance of a class of parallel algorithms on a variety of MIMD parallel machines.