This article examines the theoretical basis of how one determines whether a person is sufficiently connected to a state in order for an obligation to pay tax to that state to arise. It focuses primarily on the taxation of individuals and the theoretical underpinning of the connecting factors used to impose tax on individuals. The article outlines the various types of theory of taxation and their historical origins and development, including the benefit theory, the theory of economic allegiance and the ability to pay theory, and examines each as a candidate theory for defining and analysing connecting factors in taxation. The article argues that none of the principal taxation theories gives a good account of, or provides a sound theoretical basis for, determining how a person’s connection to a state should be determined for tax purposes and proposes an alternative theory, the membership theory of taxation, which is then outlined and discussed.