Building on John Ruggie's pioneering study of multilateralism, this paper presents an analogous study of multistakeholder governance, or multistakeholderism. Its central argument is that multistakeholderism is, as yet, a much less well-defined institutional form. Cases exhibit significant variation both in the combinations of actor classes entitled to participate and the nature of authority relations among those actors. The first section discusses multistakeholderism as an institutional form, and proposes a taxonomy of its types. This section also briefly addresses the implications of the analysis for International Relations theory. The paper then conducts a comparative analysis of multistakeholderism, applying the taxonomy to five illustrative cases. It demonstrates the degree of inter-case variation, and the range of issue-areas across which the institutional form is employed and invoked by actors. Three cases are drawn from the increasingly contentious area of Internet governance; the paper thus makes a secondary contribution to this growing literature. The paper's most striking finding in this regard is that Internet governance often fails to live up to its multistakeholder rhetoric. Other cases include governance of securities regulation and the governance of corporate social responsibility. The paper concludes by examining the implications of our argument, and identifying areas for further research.