Building on John Gerard Ruggie’s pioneering study of multilateralism, this paper presents an analogous study of multi-stakeholder governance, or multi-stakeholderism. Its central argument is that multi-stakeholderism 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 multi-stakeholderism 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 authors then conduct a comparative analysis of multi-stakeholderism, applying the taxonomy to five illustrative cases, demonstrating the degree of inter-case variation and 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, thus making 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 multi-stakeholder rhetoric. Other cases include governance of securities regulation and the governance of corporate social responsibility. The paper concludes by examining the implications arguing multi-stakeholderism is a less defined institutional form, and identifying areas for further research.