Publisher Summary The word transistor is an abbreviation of two words transferring and resistor. The chapter discusses the basic principles of transistors and biasing of transistors. The objective transistor biasing is to try to maintain the chosen operating point with changes in supply voltages–this is particularly true of battery operated equipment where the supply voltage changes considerably as the battery discharges. Further, the chapter provides review of field effect transistors; there are two main types of field effect transistors; the junction FET or JFET, and the metal oxide silicon FET or MOSFET. MOSFETs are sometimes also referred to as insulated gate field effect transistors, IGFETs. A high electron mobility FET is also known as I-IEMFET. This chapter reviews the operating principle of bi-polar transistors FETs and MOSFETs. It also reviews some transistor biasing methods.