This article explores institutional and other factors facilitating the substantive representation of women in parliament. It engages with a range of indicators of substantive representation, including process/ responsiveness indicators, legislative/policy outcomes and attitudinal alignment of women representatives and women in the community. It presents an Australian case study of a successful initiative by a cross-party group of women parliamentarians to facilitate access to the abortion drug RU486. It finds that critical mass, critical actors and a critical juncture were important but so was institution-building, particularly the understudied role of parliamentary groups.