This transformative guide completely breaks down our current understanding of biological sex and gender diversity. Introducing readers to seven variations of human sex, commonly considered intersex, the book challenges the myth that sex and gender are exclusively binary and explores the inherent diversity of biological sex and its relationship to gender identity and expression, and the impact this has on society. Examining historical, linguistic and socio-cultural understandings of sex and gender, as well as genetic and scientific definitions, the book is an important resource for dismantling gender and sexuality-based discrimination and promoting understanding and inclusivity. Co-written by one of the world's leading intersex activists and a highly respected scholar in biological sciences, and accompanied with detailed anatomical illustrations throughout, this pioneering text is the essential introduction to gender and sex diversity for gender studies, women's studies, biology and genetics courses, as well as professionals working with intersex and trans communities.