  We demonstrate that the use of on-shell methods, involving calculation of the
discontinuity across the t-channel cut associated with the exchange of a pair
of massless particles, can be used to evaluate loop contributions to both the
electromagnetic and gravitational scattering of massive systems. In the
gravitational case, the use of factorization permits a straightforward and
algebraic calculation of higher order scattering results, which were obtained
previously by much more arduous Feynman diagram techniques.
