This book defends the thesis that Kant's normative ethics and his practical ethics of sex and marriage can be valuable resources for people engaged in the contemporary debate over same-sex marriage. It does so by first developing a reading of Kant's normative ethics that explains the way in which Kant's notions of human moral imperfection unsocial sociability inform his ethical thinking. The book then offers a systematic treatment of Kant's views of sex and marriage, arguing that Kant's views are more defensible than some of his critics have made them out to be. Drawing on Kant's account of marriage and his conception of moral friendship, the book argues that Kant's ethics can be used to develop a defense of same-sex marriage.