This article aims to make a contribution to the conceptualization of mainstreaming gender equality promoted by the European Union. It starts by exploring the historical periodization of equal opportunities delivery strategies and challenging the compartmentalization of these developments. It suggests that equality policies can better be conceptualized in terms of a `three-legged equality stool', which recognizes the interconnectiveness of three perspectives — the equal treatment perspective, the women's perspective and the gender perspective. The article argues that the gender perspective has (...) been closely associated with strategies for mainstreaming gender equality, but that this association is misleading. As a result mainstreaming has remained a `fuzzy' concept, which in turn has led to many different styles and forms of practical implementation in European member states. (shrink)