Critics have argued that the field of information systems (IS) lacks a coherent theoretical framework. This paper attempts to further the theoretical development of a critical and pervasive contemporary phenomenon, outsourcing of IS functions, by synthesizing four theoretical models (resource-based theory, resource-dependence theory, transaction cost theory and agency theory) that are useful for understanding determinants of a firm's outsourcing strategy. From these theoretical models, a contingency model of outsourcing is developed which can be used to direct empirical research.