A theory of implementation for multilateral regulation of business is introduced. Four types of implementation actors (international organizations, states, nongovernmental organizations, and business associations) and three implementation tasks (communicate, monitor, and sanction) are identified. The ease of implementation is affected by issues and events that occur early in the life cycle of a policy. Ten propositions are put forward regarding the effects of problem definition and policy formulation on implementation. The theory is illustrated with the Montreal Protocol on Substances that (...) Deplete the Ozone Layer. (shrink)