This chapter describes circuit parameters that are based on power flow. The open-circuit Z-parameters and the short-circuit Y-parameters are used in many of the circuit computer-aided design (CAD) programs. We can calculate the network parameters of circuits made from well-known components such as resistors, capacitors, and inductors. However, the circuit parameters of transistors and other types of semiconductors must be measured. As frequencies rise, it becomes increasingly difficult to measure voltage and current on the ports of a circuit.