Classical Control is the set of methods and procedures for designing control systems that were developed around the time of the World Wars, ending in 1960. These types of controllers are still some of the most used today because of their simplicity and the maturity of the design methods. Development of these control systems took place in research labs such as Bell Labs, the MIT Radiation Lab, and Military Labs. Many applications still use Classical Control as the basis for controlling systems for practical and historical reasons. For many simple applications, classical design methods are quick and easy to use with well-known metrics for performance, robustness, and stability. Historically fields such as aerospace engineering have their roots in the design of aircraft using classical control techniques and continue to use many methods, if not for design then as a method of describing the systems simply and concisely. In order to work with control systems, a solid understanding of classical control is necessary. Far from being out-dated, it is still used in many applications and is the source of much of the language and metrics used to describe even the most complicated systems.