The concept of 'women's interests' has received a large amount of scholarly attention. In particular, the problematic assumption underpinning this concept - that women share interests - has been an object of much consideration. Yet, while scholarship on the substantive representation of women has today moved free of this assumption, three other assumptions have not been scrutinised to the same degree. These are: (1) that political interests are attached to social groups; (2) that women and men have different interests; and (3) that there are only two genders. This article argues that these three assumptions are problematic for feminist scholarship on substantive representation, which warrants replacing the attached 'women's interests' with an alternative interest: the unattached 'gender equality interests'. In addition, the article sets forth three distinct ways for future studies to operationalise the substantive representation of gender equality.