A new definition of woman has taken hold in Western societies. Instead of a matter of biology and material reality, we are told it is an identity. Anyone who declares herself to be a woman is a woman; the body has henceforth become irrelevant. Gender, we are told, is a spectrum, and it resides in the mind. In countries such as Norway, Canada, Argentina, and Australia, laws have been enacted that give anyone the right to change his or her legal sex, irrespective of whether the person has had a medical procedure. At the same time, the industry for gender reassignment surgery is growing at an unprecedented pace. Seven out of 10 teenagers who seek treatment are now girls. The new definition of sex has been hailed as progressive. But is it really? And is it new? In this groundbreaking book, Swedish feminist and Marxist author Kajsa Ekis Ekman traces the ideological roots of this new definition.