How are sex and gender related? Are they the same thing? What exactly is gender? How many genders are there? What is the science on all of this? Is gender a product of nature, nurture, or both? This book introduces readers to fundamental questions about sex and gender categories as they’ve been considered across the centuries and through a wide array of disciplines and perspectives. From the Bible to Darwin, from Enlightenment thinkers to contemporary trans philosophers, offers an accessible survey of the wide range of views about sex and gender. This revised and expanded edition uses updated terminology and diagnostic criteria and offers new material with a greater focus on trans, Indigenous, racialized, and subaltern thinkers. It includes useful discussion questions and further reading recommendations at the end of each chapter, as well as an extensive glossary of terms.