Fabricating a CMOS chip begins with a layout from which photomasks are made. But where does the layout come from? The layout is, in fact, the endpoint of the design process. CMOS chips contain billions of components. Thus, however entertaining it might be to imagine, we cannot expect the designer to manually draw the entire chip layout. In fact, producing the layout is mostly an automated process. The designer, at least at face value, produces a much higher-level description of the circuit, and tools translate it into a layout. This description, and the automation of the process are very misleading. As this chapter will show, if the designer is not aware of what each step of the automated flow is doing, the flow is almost guaranteed to not produce a working chip.