This article aims to explain the differential use of litigation by social movements pursuing social change. While previous studies have sought to compare non-governmental organizations (NGOs) that turn to litigation with those that do not, we study organizations that have all resorted at least once to legal action. Taking Belgium and the field of antidiscrimination as a case study, our research confirms the findings of previous literature that the characteristics of the legal environment do impact on the choice of organizations whether or not to go to court. But we also find that legal action is used differentially by NGOs depending on two factors in particular: their position as an insider or outsider in the political realm and their possession of legal resources. Based on a quantitative measure of legal actions initiated by NGOs and interviews with activists, we propose a typology of civil society organizations—which we label “experienced litigants,” “occasional litigants,” and “litigants by necessity”—that could be transposed to other contexts and other types of interest groups.