This paper described a computer program--DYMAC--which finds displacements, velocities, and accelerations in planar machinery subjected to forces of a virtually unrestricted nature. The user may also specify the motion of any parts of the system (e.g. speed of a crankshaft), and prescribe general relationships between the motions of different points in the system, as illustrated by an example of a spring-suspended vehicle moving over a rough road. It is shown how the information which describes the geometric, inertial, and topological properties of the system must be organized. Readers should be able to determine if DYMAC will serve their needs.