  We delineate the role of rotation and spin in physics, discussing in order
Newtonian classical physics, special relativity, quantum mechanics, quantum
electrodynamics and general relativity. In the latter case, we discuss the
generalization of the Kepler formula to post-Newtonian order $(c^{-2}$)
including spin effects and two-body effects. Experiments which verify the
theoretical results for general relativistic spin-orbit effects are discussed
as well as efforts being made to verify the spin-spin effects.
