Dutch development agencies were among the frontrunners and promoters of gender mainstreaming from the mid-1990s. In this article, we reflect on their experiences of mainstreaming gender, and argue that procedural approaches need to be complemented with more substantive approaches. We trace the resourcing of gender mainstreaming policies in Dutch development agencies, and reflect on the strengths and weaknesses of commonly used instruments, targets, and gender assessments. Our lessons are based on a collaborative learning programme involving practitioners, policy makers, and academic researchers.