The chapter provides an overview of (fluctuations in) NGO access to intergovernmental organizations (IGOs) since 1815. It starts with the major background, the rise of civil society as part of changes in the Westphalian system of states. It then focuses on the open multilateral system of the nineteenth century, paying attention to the emergence of both INGOs and IGOs, the also fairly open League of Nations system and the more limited but eventually widening United Nations system and other IGOs. Finally, it discusses theoretical explanations, among them Jens Steffek’s push and pull factors regarding NGO–IGO cooperation. The many instances of access to and NGO involvement in IGOs before 1945 do not justify the claim by Tallberg et al. (in The Opening Up of International Organizations, 2013) that IGOs were too long ‘the exclusive preserve of member governments’, with only fairly recently a change toward more complex forms of governance.