This article sets out to chart the evolving institutional structure of the EU, in the context of theories about forms of state. ‘Forms of state’ are taken to be conceptually possible expressions of political authority organized at the national and transnational levels, here dealt with as emphases and qualities to be accented rather than phenomena to be sorted into categories. The EU is examined in the light of three stylized state forms - the Westphalian state, the regulatory state and the post-modem state. Each of these captures important elements of the evolution of the EU, and provides support for analysis of its development as a form of ‘international state’. Such an analysis implies attention not only to forms of state, but also to related concepts such as government and governance which give leverage on the exploration of ‘international state forms’. Conclusions are drawn about the power of the three ‘metaphors’ used, and the relationship to possible empirical studies.