What Is Marriage? Man and Woman: A Defense is a 2012 book co-authored by Sherif Girgis, Ryan T. Anderson, and Robert P. George, presenting a philosophical and legal defense of traditional marriage as a conjugal union between a man and a woman. The authors argue against same-sex marriage by outlining the 'conjugal view' of marriage, which emphasizes procreation, sexual complementarity, and the comprehensive union of spouses, contrasting it with the 'revisionist view' that prioritizes emotional bonds and individual autonomy. The book draws on natural law theory, historical precedents, and public policy implications, asserting that redefining marriage harms children, society, and religious liberty. It has been influential in conservative intellectual circles, cited in U.S. Supreme Court briefs during marriage equality debates (e.g., Obergefell v. Hodges), and praised by figures like William F. Buckley Jr., while criticized by LGBTQ+ advocates for promoting discrimination.