Apparently, present-day global governance is lacking legitimacy, mainly because it is not democratic. What role, then, may (international) civil society – amongst others mainly NGOs and INGOs – play to make global governance more democratically accessible and accountable, and thus more legitimate? What role may we allow these actors to play? What role should – and shouldn't – these actors have? Against the background of inherent shortcomings and problems of mostly representative forms of democracy of today, globalization and the rise of all sorts of global problems, this thesis develops a multi-indexical concept – or framework – of legitimacy which aims at judging international civil society actors as either legitimate or illegitimate. This multi-indexical concept of legitimacy mainly focuses on NGOs' and INGOs' performance helping to mend some of the aforementioned democracy-inherent problems, providing solutions for some of the most pressing global problems and, finally, making global governance more accessible and democratically accountable. NGOs and INGOs may also be considered legitimate because of their long-term objective, the global common good. Apart from this, this thesis also looks into alternative forms of mandating political representatives apart from elections, and non-majoritarian forms of decision making.