This article discusses the Europeanization of social movement organizations using the case of ILGA-Europe, the umbrella of lesbian, gay, bisexual, and transgender organizations in Europe. It examines the impact of Article 13 of the Treaty of Amsterdam, which bans discrimination on the grounds of sexual orientation, and focuses on three entrenched dynamics ILGA-Europe has rapidly undergone: NGOization, institutionalization, and professionalization. It argues that although we should be aware of the role of the European political opportunity structure in shaping civil society organizations, we cannot overlook internal organizational dynamics and movement identities. Following the literature on the Europeanization of social movements, this piece confirms institutional opportunities and interactions with European institutions are a major cause of transformation: The adoption of Article 13 and the development of a European equal opportunity policy constitute a pivotal moment in ILGA-Europe’s history, endowing it with easier access to EU institutions and core funding. This allowed the organization to NGOize, contributed to a transformation of its internal structures, and led to the appointment of highly skilled professionals. However, this article also insists on the importance of movement identity. These transformations are not solely the result of interactions with the European institutional environment, but had been prepared by long-term orientations within ILGA, that is a preference for reformist claims and institutional strategies. ILGA-Europe’s NGOization is thus not only a response to institutional and political changes, but also results from specific ways of imagining activism. It is the interaction between movement identity and arising institutional opportunities that allowed the organization to transform.