This section gives an overview of the integrated circuit technology. Semiconductor devices and circuits are formed in thin slices of a material (called a wafer) that serves as the substrate. For proper operation of the device/circuit, the substrate material must have crystalline structure where all the atoms are aligned in a specific pattern. In the first section of this chapter, the structure and growth of crystals are discussed. The next section deals with the cleaning of wafers which is an important step in the fabrication of integrated circuits. One of the basic building blocks in integrated circuit processing is the ability to deposit thin films of material. A large number of deposited films by wide variety of techniques are used in integrated circuits. These films can either be grown on semiconductor or deposited by various techniques. Most films can be formed by more than one method. Thermal Oxidation of Silicon is taken up first because it is an important step which is often repeated throughout the IC fabrication. This is followed by other principal film deposition techniques such as vacuum evaporation, sputtering and chemical vapor deposition. The properties of the films or substrate can be modified by process like diffusion and ion implantation and they enable to form a variety of devices in integrated circuits. A brief description of diffusion and implantation process and systems are given in section 4. In the subsequent section the lithography process is treated. The basic approaches to CMOS fabrication such as the p-well, the n-well, the twin tub and silicon on insulator processes are discussed in section 6. Very brief discussion on the fabrication of passive components also included. This chapter ends with a discussion on latch up and technology related CAD issues. In summary, an integrated circuit process is usually a structured sequence of operations such as the ability to deposit/modify thin films on the substrate, to apply a patterned mask on the films by photolithographic process, and to etch the films selectively to form actual devices.