This chapter deals with the devices and circuits that comprise the electronic amplifiers of linear systems used in instrumentation applications. The discussion begins with the temperature limitations of semiconductor devices and is extended to differential amplifiers and an analysis of their parameters for understanding operational amplifiers from the perspective of their internal stages. This includes gain–bandwidth–phase stability relationships and interactions in multiple amplifier systems. An understanding of the capabilities and limitations of operational amplifiers is essential as a preface to instrumentation amplifiers.