Biology of Sex is a lively and intellectually challenging textbook. Mills analyzes the biological basis of sex by considering genetic, physiological, and evolutionary principles. In order to explain the biological aspects of human sex, he uses direct and intriguing comparisons with the many variations in sexual systems among non-human organisms. Text boxes provide fascinating examples: non-human species that cannibalize their partners during copulation, organisms that do not fall within one of two biological sexes, and species that “trick” others into raising their young. The author also explores questions such as: “Is sex only for reproduction?”, “Why is sex pleasurable?”, and “What are the roots of sexual conflict?” Intended primarily for readers without a science background, Biology of Sex provides novel content from the human and non-human worlds to introduce the complex subject of sex and reproduction.