Computer-aided analysis and simulation was once considered practical only in high technology or high cost industries. However, the advent of personal computers has given simulation a new dimension and made hydraulic system simulation a viable addition to the design process in many industries. The FESIM package, presented in this paper, is a PC CAD tool for hydraulic system design and analysis which allows engineers to simulate and analyze hydraulic circuits, substitute components, vary design and/or operational parameters, and observe the performance (flow, pressure, temperature, etc.) of a system at every point in the circuit. Both the underlining principle of FESIM and numerous applications are illustrated.