This chapter shows that the concept of network functions is obtained as an extension of the element defining equations for resistors, capacitors, and inductors. Network functions are employed to characterize linear, time-invariant networks in the zero state for a single excitation. Network functions contain information concerning a network’s stability and natural modes. The concept of impedance can be extended to linear, lumped, finite, time-invariant, one-port networks in general. The chapter provides techniques, strategies, equivalences, and theorems for simplifying the analysis of lumped, linear, finite, time invariant (LLFT) networks or for checking the results of an analysis. Superposition is a property of all linear networks, and whether it is used directly in the analysis of a network or not, it is a concept that is valuable in thinking about LLFT networks. Thevenin’s theorem is useful in reducing the complexity of a network so that analysis of the network for a particular voltage or current can be performed more easily.