This documentation describes the Java application programming interface to Ssim, a very simple discrete-event sequential simulation library. The simulator implemented by ssim executes reactive processes. These processes are defined in terms of discrete execution steps performed at given times, or in response to an interaction (an event) with another process. During the execution of an action, a process may schedule other future actions for itself, or it may signal events to another processes, which will respond by processing the signalled events at the given time. The simulation terminates when no more actions are scheduled.