In Christian traditions, “natural law” names the moral impulses, principles, or judgments shared by all human beings as rational creatures of the one God. It was formulated influentially by Thomas Aquinas. Through Thomas, it became a fundamental notion in Catholic moral theology, but also in philosophical ethics and international law. Despite early rejections, natural law was also taken up by Protestant thinkers, notably in Anglicanism by Thomas Hooker. In the last decades, it has been cited in public debates over a range of controversial issues, from artificial contraception to torture and nuclear war. This seminar will take up important treatments of natural law—first in Thomas Aquinas, then in his early modern interpreters, and finally in recent American debates.