Across Europe, contention has emerged over the Istanbul Convention, a treaty combatting violence against women. The Convention has become a main arena for contention over gender and sexual equality. Right-wing forces mobilize nationally—and transnationally—to advocate for traditional values and oppose so-called ‘gender ideology’, while progressive actors resist efforts to curtail women’s rights. Consequently, while many have ratified the Convention, several countries have not. This article asks which causes motive ratification; which causes underlie non-ratification? We present a qualitative comparative analysis (QCA) on 40 European states to disentangle the causal complexity of ratification decisions. We identify four pathways for ratification, driven by feminist egalitarian norms, international conditionality, pro-European governments at odds with social opposition, and societies unwilling to mobilize for conservative religious institutions. We unpack these causal patterns in four minimalist case studies. The article reveals causation underlying contention between pro-gender, anti-gender, and state actors, and resultant policy outcomes.