Orbital dynamics is primarily concerned with the motion of orbiting celestial and man-made bodies. A well-studied specific orbital dynamics problem is the classic two-body problem, where two celestial bodies keep moving under the gravitational influence of each other. This chapter presents an overview of the two-body orbital mechanics first. Satellite orbital dynamics is presented next, which is a special case of the two-body problem, where the mass of one celestial body (e.g., the satellite) is negligible as compared to the body around which it orbits. Subsequently, the relative motion of two satellites is presented, which is used to synthesize the guidance schemes for formation flying.