A comprehensive review of the S-parameter theory is given from the viewpoint of symbolic analysis. S-parameters are proposed to characterize arbitrary networks in t he most general sense. An algorithm is developed to calculate S-parameters symbolically. The original program SPAR is presented, which is intended for automated computer-aided symbolic derivation of S-parameters of time-invariant linear networks . The original program SALEC is used as an engine in SPAR to find the circuit response symbolically. A real life example is given to illustrate the application of symbolic analysis in the field of automated microwave network analyzer measurements.