We use self-consistent mean field methods and analytical theory to determine the behavior of AB copolymers at the interface between two incompatible homopolymers, A and B. We calculate the reduction in interfacial tension, gamma, resulting from the copolymers localizing at the A/B interface. We examine the effects of chain length, composition, and molecular architecture on the efficiency of the copolymers. In particular, we compare the interfacial behavior of different linear copolymers (random, alternating, and diblock) and various branched copolymers (stars and combs). At fixed molecular weight, the diblock copolymers are the most efficient at reducing gamma. However, when we compare random and comb copolymers with diblocks at different molecular weights, we observe that the longer random or comb copolymers are more efficient than short diblocks. These studies allow us to predict the reduction in interfacial tension produced by a wide variety of copolymers and, thereby, permit a rational design of cost-effective and efficient compatibilizers.