The need for hybrid simulation arises with higher operating frequency and miniaturization of the electronic systems. During the past decades, elaborate simulation schemes have been developed for various lumped-in-nature systems, without worrying much about the electromagnetic field effects. Generally speaking, the field effects already start to take their toll on the "ideal" circuit performance; they have not been fully characterized because most of the current circuit simulators do not have the ability to efficiently take them into account. For fair comparison, some of the parasitic field effects, mostly static, are included in the circuit simulation through the elaborate model extraction. As mentioned in earlier chapters, a detailed circuit component and packaging model could include some of the effects into simulation; other used-to-be ideal elements such as the connecting metal wires, start to demonstrate their distributive nature, namely inductive effect, line delay and coupling.