This introduction presents an overview of key concepts discussed in the subsequent chapters of the book. The book explores the harms created by the ideology and practice of transgenderism, a phenomenon that developed in the mid to late twentieth century. It examines the construction of transgenderism by medical specialism such as endocrinology, surgery and psychology. The book examines the most immediately harmful impact of the construction of transgenderism. It analyses the literature on the psychological and physical effects of transgender surgery and long-term hormone use on transgenders themselves. The book describes the harmful practices involved in transgender practice from breast binding to genital surgery, and repeated facial surgeries, and who profits from them. It argues, from a feminist perspective, that transgenderism is but one way in which 'gender' hurts people and societies.