This book addresses the opposing positions held by Catholic orthodoxy and modern liberal societies on questions about human sexuality, marriage and family life. The author argues that true to the nature of doctrine, some moral teachings are open to development and some dogmatic ones are irreversible. In five chapters, relying on historical analysis, a hundred-year timeline is used to examine related papal encyclicals. A review of the natural law theory from its Stoic antecedents, Thomistic scholasticism, and the philosophical 20th-century new natural law theory are examined. John Paul II¿s Theology of the Body is used as a subtext. Intellectual, cultural and gendered perspectives are put in dialogue while paying attention to two current issues; same-sex unions as sacramental unions and the possibility of the use of condoms as prophylaxis for discordant married persons. This work appeals to both specialists and non-specialists, scholars, students of theology and those who are interested in matters concerning the development of Christian [moral] doctrines. It can be used as a whole or in chapters for private studies, classroom work or in pastoral settings.