This book establishes that normativity has necessary characteristics explicable only through the natural law formulation developed by Aquinas and based on loving God and neighbor, albeit understood in terms other than Christian charity and updated according to the personalism of John Paul II. The resulting personalist natural law can counter objections rising from classical and contemporary metaethics, moral diversity, undeserved suffering, antithetical interpretations of Aquinas's natural law, and alternative ethical theories, e.g., atheistic eudaimonism. Also established are the virtues of love; the nature of indefeasibility, moral objectivity, human flourishing, and Thomistic self-evidence; the relationship between the Bonum Precept (good is to be done and pursued; evil is to be avoided) and the love precepts (God is to be loved above all; neighbors are to be loved as oneself) as well as specific moral and legal obligations. These specifications update the nature of the common good, Just War Theory, the warrant for capital punishment, environmental obligations, and the basis for universal, unalienable rights, including religious liberty. The Appendix sketches the history of natural law from its origins in ancient Greek philosophy and Roman law, through developments during the Enlightenment and the American revolution, to contemporary incarnations. Overall, the book's scope and detailed arguments make it a comprehensive resource for those interested in normative foundations, justifying morality's objectivity and universality, global jurisprudence, and recasting Thomistic natural law in terms of personalist love.