This chapter considers the laws governing the overall motion of a system consisting of a finite number of interacting particles. The system’s center of mass, linear momentum, and angular momentum are defined. Assumptions regarding the interactions between the particles and Newton’s second law lead to the system’s equations of linear momentum and angular momentum. It is further shown that the angular momentum equation also holds for a coordinate system that is translated with the center of mass, even though it need not be inertial. Next, the balance of work and kinetic energy is considered, and it is shown that the internal forces do not perform work in a rigid system.