Who counts as a woman? This question lies at the heart of many public debates about sex and gender today. While we increasingly recognise the desire of some to eliminate the sex binary in law, a particular boiling point emerges through conflicting demands over women’s spaces. Which should govern access to these – sex or gender identity? Karen Ingala Smith, a veteran campaigner for women’s and girls’ rights, opts for the former. In this trenchant critique of inclusivity politics, she argues that we cannot ignore the wealth of evidence which shows that people of the female sex have a unique set of needs which are often not met by mixed-sex spaces. Drawing on her 30 years of experience in researching and recording men’s violence against women and girls, she outlines how certain spaces, including refuges, benefit from remaining single sex – and what they stand to lose. Written with sensitivity and respect for all concerned, this book nevertheless dismantles the idea that we have reached a post-sex utopia.