Proper pretreatment and surface preparation is an essential first step in the finishing process. In designing a pretreatment system, consideration must be given to the level of quality required, the production quantities that must be handled, and the acceptable levels of capital and operating costs. This paper reviews the chemistry and equipment required to pretreat both metal and plastic substrates for spray, electrocoating, or autodeposition and discusses how to design an automated pretreatment system to ensure optimal finish quality by maintaining consistency in washer chemistry and cleaning processes.