Over the past fifteen years, substantive equality and the idea of positive measures to tackle the structural roots of gender inequality have increasingly gained currency in Europe. Focusing on the case of Greece, this article explores the factors that promote constitutional and statutory reforms to promote substantive equality, and examines the effect of such reforms on gender equality rights and policy. It argues that domestic legal and social mobilization by feminists, who participated in transnational networks, were instrumental in the diffusion of the relevant EU and international norms, leading to a shift in the courts’ jurisprudence and to a constitutional amendment recognizing substantive equality. At the same time, the paper also underscores the ambivalent and limited effects of constitutionalizing substantive equality and positive measures in the absence of ongoing actions aimed at raising awareness and pushing for effective implementation.