Whether we love them or hate them, think they're sexy or weird, consider them too big or too small or the complete opposite, humanity has a complicated relationship with butts. It's a body part that only our species possesses, key to its evolution and survival, and yet it has come to mean so much more: sex, desire, humor, shame. This cultural history takes us from the showrooms of 19th-century London to the aerobics studios of the 1980s, from Sir Mix-a-Lot's Baby Got Back to the mountains of Arizona, where humans and horses compete each year in a feat of gluteal endurance. From evolutionary biologists studying how the first butts developed, to models whose measurements have defined jean size for millions of women, to fitness gurus who created trends, this book also shines a light on racial bias through figures such as Sarah Bartmann, Josephine Baker, Jennifer Lopez, and other women whose behinds have been idolized, envied, and scorned. Part deep investigation, part personal journey, and part cabinet of curiosities, this is an entertaining, revealing, and thoughtful exploration of why certain shapes come in and out of fashion, and how our conceptions of race, control, liberation, and power affect our perceptions of ourselves and others.