  We discuss the motion of spin in inertial and gravitational fields. The
coupling of spin with rotation and the gravitomagnetic field has already been
extensively studied; therefore, we focus here on the inertial and gravitational
spin-orbit couplings. In particular, we investigate the classical and quantum
aspects of spin precession and spin-orbit coupling in an arbitrary
translationally accelerated frame of reference as well as the exterior
Schwarzschild spacetime. Moreover, in connection with Einstein's principle of
equivalence, we clarify the relation between the inertial and gravitational
spin-orbit couplings.
