Mechanical separation usually involves the use of several types of unit processes, five of which are size reduction, screening, air classification, magnetic separation, and non-ferrous (e.g., aluminium) separation [1-5]. Table VI-2 lists unit processes relevant to separation, as well as most of the types of mechanical unit processes that have been incorporated into waste processing facilities implemented to date. The sequence of the processes for mixed waste processing varies, although either size reduction or a preliminary screening (trommel) usually is the first step. Process design is described later in this chapter. The intent of this section is to present a brief overview of the equipment; in-depth discussions can be found in Reference 1