This Element presents the rudiments of Thomas Reid’s agency-centered ethical theory. According to this theory, an ethical theory must address three primary questions. What is it to be an agent? What is ethical reality like, such that agents could know it? And how can agents respond to ethical reality, commit themselves to being regulated by it, and act well in doing so? Reid’s answers to these questions are wide-ranging, borrowing from the rational intuitionist, sentimentalist, Aristotelian, and Protestant natural law traditions. This Element explores how Reid blends together these influences, how he might respond to concerns raised by rival traditions, and specifies what distinguishes his approach from those of other modern philosophers.