Abstract
Policy debates have focused on who can participate in or access single-sex activities or services. This article describes how science of the biology of sex is relevant to three major policy areas: parenting (including leaves), sports, and public spaces. We focus on what scientists know about sex and gender (and gender/sex, where gender and sex are intertwined), and the role of various biological factors, including hormones such as testosterone and estradiol as well as genetics, gonads, genitals, and more. The policies under debate often use “biological sex,” but this fails to account for scientific understandings of sex and gender, misrepresents sex as single-faceted and binary, and overlooks scientific consensus about the importance of gender and identity.