This working paper introduces the concept of legal personality of non-state actors as an indicator of the democratic legitimacy of international organizations (IOs). Globalization has led to changes in statehood which are reflected in new democratic forms of participation and new expectations and attitudes towards political institutions. This also affects international politics in that international organizations are questioned with regard to their own legitimacy. In this context, normatively and empirically based policy proposals alike tend to suggest an increased role of new actors, mostly civil society organizations (CSOs) or NGOs, in overcoming the legitimacy deficit of IOs. However, if participation of non-state actors in international governance is to be effective, efficient and have a meaningful and lasting effect, it requires institutional rights and duties - and with it legal personality. Thus, legal personality of non-state actors can be taken as a minimum safeguarding clause for surmounting the legitimacy deficit of international organizations (normative approach). It can also be used as a helpful analytical framework for organizing empirical data on the participation of these actors in IOs (empirical approach). This working paper evaluates the legal rights and duties of NGOs in their cooperation with more than 30 international organizations and seeks to assess whether this implies that they have acquired legal personality and which quality this personality takes on. Such a comparative paper is a novelty in both political science and international law. By combining perspectives from two disciplines, this working paper illustrates the intrinsic empirical and theory-building value of (international) positive law in political science.