Transgenderism is the focus of vigorous public debate at present. Questions as to the relative significance of gender identity and physical sex and what it means to be trans are at the heart of arguments about whether transwomen should compete as women in sports, whether medical intervention is appropriate for young teenagers who don’t identify with their sex, who should be in women’s prisons and how public debate should be conducted. The courts are increasingly asked to grapple with these questions. However, guidance produced by the Judicial College is surprisingly committed to some of the ideas and claims that are in dispute.