This chapter ^[1] describes the steps and processes used in realizing modern integrated circuits. Although emphasis is placed on CMOS processing, the technology required for bipolar-junction transistor (BJT) circuits is also described. After processing is presented, circuit layout is covered. Layout is the design phase in which the geometry of circuit elements and wiring connections is defined. This stage leads to the development of photographic masks, which are used in manufacturing a microcircuit. The concepts of design rules and the relationship between the rules and the microcircuits are emphasized. Next, circuit layout is related to the transistor models. Here, it is shown that once the layout is completed, the values of certain elements in the transistor models can be determined. This knowledge is necessary for accurate computer simulation of integrated circuits. It is also shown that by using typical design rules, reasonable assumptions to approximate transistor parasitic components can be made before the layout has been done. The chapter concludes with a brief description of more modern processing techniques.