Since the end of the eighteenth century and throughout the nineteenth century, there have been many proposals for internal combustion engines. Most of them were unsuccessful, but finally, in 1876, N. Otto developed the engine that became the starting point for all modern internal combustion engines. In this engine, the intake valve was of the sliding type and the exhaust valve was a mushroom valve, but both were driven by a camshaft. Soon, cam-driven mushroom valves became the norm. Since then, billions of cams have been manufactured to drive the valves of internal combustion engines. Cams have the advantage of allowing you to choose not only the length of the valve lift, but also the law of motion. This has a major impact on engine behavior and performance. The law of motion, and therefore the cam profile, is divided into three parts. Two parts are associated with the active phases of valve opening and closing, and the third part is associated with the intermediate phase when the valve is closed. It is possible to add a fourth part in order to keep the valve open for a certain period of time. The first classical texts outlined cams with circular arc profiles and straight segments. Much more refined laws have since been adopted, but the problem of choosing the law of motion is beyond the scope of this book. Diesel engines use high-pressure injection pumps that use cams. Today, many gasoline engines also use fuel injection and cam-driven pumps. Therefore, these pumps are also mentioned here.