This chapter explores the requirements and general characteristics of digital logic gates. Subsequent chapters investigate the detailed implementation of logic gates in both MOS and bipolar technologies. The initial discussion in this chapter focuses on the characteristics of the inverter. Important logic levels associated with binary logic are defined, and the concepts of the voltage transfer characteristic and noise margin are introduced. Later, the temporal behavior and time delays of the gates are addressed. A review of Boolean algebra, used for representation and analysis of logic functions, is included, and simple AND gates, OR gates, and NAND gates are implemented using diode logic and bipolar transistors.