This chapter provides an investigation of the basics of designing and characterizing logic gates in an metal-oxide-semiconductor (MOS) technology. The properties of digital logic gates are derived from a large-signal analysis of the circuits. Because transistor characteristics are intrinsically nonlinear, accurate analytic modeling becomes quite complicated, and closed-form solutions can be difficult to come by. Once the basic operation is established, computer simulations are used to obtain more accurate information. Square-law models are useful for understanding the operation of MOS logic circuits. In digital circuit design, it is useful to model Metal–oxide–silicon field effect transistor (MOSFET) as voltage-controlled switches. Early generations of MOS logic circuits were based on a single type of MOSFET. Static logic gates are based on the inverter. Canonical CMOS static logic design is based on using pairs of N-channel MOSFET and P-channel MOSFET transistors. Transmission gates provide another approach to implementing logic functions in CMOS.