This chapter explores the concept of natural law, turning first to the Protestant milieu. Alterity—what would in the seventeenth century come to be theorized, and problematized, as “sociability”—is the dominant mood of the humanist and Protestant handling of natural law. It is there even in Thomas Hobbes, whose natural law coincides with moral philosophy and concerns the sphere of one's actions in respect of others. However, the Catholic scholastic tradition presents a very different framing of natural law, one that centers on individual agency and regulates the behavior of individual agents in their aspect as beings of a particular kind. While authors in this tradition grapple equally with the question of animal behavior in relation to law, they do not do so from the social perspective that characterizes Protestant humanist Aristotelians and jurists.