Over the last two decades, but particularly in the last 10 years, research into sex, gender and politics has become an established sub-field of political science. This article opens with some reflections on the position of 'women and politics' scholars and research within the British political science community. It then moves on to reflect upon the burgeoning literature on women's political representation. In particular, it questions the way in which the relationship between women's descriptive and substantive representation has been operationalised and investigated in empirical research, namely through the concept of critical mass. Seeking to reframe these debates, the article suggests that future research should focus not on the question of when women make a difference, but on how the substantive representation of women occurs.