There is a long tradition of bioethical reasoning within the Roman Catholic faith, a tradition expressed in scripture, the writings of the Doctors of the Church, papal encyclical documents and reflections by contemporary Catholic theologians. Catholic bioethics is concerned with a broad range of issues, including social justice and the right to health care, the duty to preserve life and the limits of that duty, the ethics of human reproduction and end-of-life decisions. Fundamental to Catholic bioethics is a belief in the sanctity of life and a metaphysical conception of the person as a composite of body and soul. Although there is considerable consensus among Catholic thinkers, differences in philosophical approach have given rise to some diversity of opinion with respect to specific issues. Given the influential history of Catholic reflection on ethical matters, the number of people in Canada who profess to be Catholic, and the continuing presence of Catholic health care institutions, it is helpful for clinicians to be familiar with the central tenets of this tradition while respecting the differing perspectives of patients who identify themselves as Catholic.