This book is the first to present a comprehensive historical picture of the modern Catholic concern with the body and sexuality. The Catholic church is commonly believed to have always opposed birth control and abortion throughout the centuries. Yet the Catholic encounter with modern sexuality has a more complex and interesting history. What was the meaning of sexual purity? Why did eugenics matter to Catholicism? How did the Society of Jesus interpret the idea of overpopulation? Why did Pius XI decide to issue the notorious encyclical Casti connubii on Christian marriage - the first modern papal pronouncement on birth control, abortion, and eugenics? In answering these questions, Lucia Pozzi uncovers new archival and unpublished records to dig into Catholic responses to modern sexual knowledge, showing the Catholic church at times resisting, but also often welcoming, scientific modernity.