Dynamics of NGO legitimacy: how organising betrays core missions of INGOs

International non-governmental organisations (INGOs) are prominent actors in the international arena, aiming to improve the life of disadvantaged people. However, INGOs often do not succeed in doing this. Consequently, INGO legitimacy is regularly questioned. Increased transparency and tightened accountability mechanisms are often-mentioned solutions to this problem. Based on an analysis of four dimensions of INGO legitimacy—normative, regulatory, cognitive and output legitimacy—we argue that this is not necessarily adequate.We conclude that INGO mission statements create a normative source of legitimacy, but that this, in itself, is not enough to ground INGO legitimacy: it also needs to be institutionalised and organised. However, as a result of power relations and resulting pressures for accountability and transparency, as defined by their external stakeholders, INGOs experience a permanent struggle to reconcile their mission with the requirements for regulatory, cognitive and output legitimacy. The more these stakeholders press for increased organisation of INGO work, the more the pursuit of the core objectives of INGOs is obstructed. We illustrate this argument with the case of the post-Tsunami humanitarian intervention