In a globalizing world, governments are not always able or willing to regulate the social and environmental externalities of global business activities. Multi-stakeholder initiatives (MSI), defined as global institutions involving mainly corporations and civil society organizations, are one type of regulatory mechanism that tries to fill this gap by issuing soft law regulation. This conceptual paper examines the conditions of a legitimate transfer of regulatory power from traditional democratic nation-state processes to private regulatory schemes, such as MSIs. Democratic legitimacy is typically concerned with input legitimacy (rule credibility, or the extent to which the regulations are perceived as justified) and output legitimacy (rule effectiveness, or the extent to which the rules effectively solve the issues). In this study, we identify MSI input legitimacy criteria (inclusion, procedural fairness, consensual orientation, and transparency) and those of MSI output legitimacy (rule coverage, efficacy, and enforcement), and discuss their implications for MSI democratic legitimacy.