Legitimacy is currently a salient topic in the International Relations (IR) literature. In an era of globalisation, discrepancies have emerged between political ideals and the realities of the global distribution of power. One significant aspect of this debate concerns the role and influence of transnational non-governmental organisations (NGOs). This article examines the issue of transnational NGOs’ legitimacy in international society. It is suggested that accusations of NGOs’ ‘illegitimacy’ often rest on a comparison between ‘legitimate’ state power sanctioned by liberal democratic norms, and ‘illegitimate’ non-state power. More pressing than the fact of non-governmental sector’s ‘non-state’ character, however, is the question of how to put effective limits on power per se in international society.