The first edition of Beauchamp and Childress'' seminal book, Principles of Biomedical Ethics, appeared in 1979. That work has been the most universally accepted statement of bioethical principles. However, its proposal has not been exempt from criticism, which has led the authors to make several modifications, redefinitions and extensions to the theoretical and methodological scope of the principles in subsequent editions. The criticisms are mainly based on what Valdes has called “the problem of principlism,” which could briefly be defined as the absence of one or more criteria for ranking the principles. By returning to the path of the founders of bioethics and reviewing the main milestones that influenced the emergence of the discipline, Valdes rethinks Beauchamp and Childress'' principlism by describing its problems and demonstrating why the epistemological and methodological aspects of it are still insufficient to address complex cases with a real degree of objectivity and impartiality. Certainly, with this book Valdes makes a relevant contribution to rethink one of the most paradigmatic approaches to the real significance of bioethics.