This chapter offers accounts of John Locke’s articulation of the natural rights theme, David Hume’s articulation of the cooperation to mutual advantage theme (along with allied ideas offered by Adam Smith), and John Stuart Mill and Herbert Spencer’s articulations of the indirect utilitarian theme. My goal here is not to provide episodes in the history of libertarian political thought. Rather, it is to flesh out philosophical themes that are central to libertarian and classical liberal theorizing — including the theorizing that will be examined in the next three chapters — whether or not each of their expositors should be classified as a libertarian or classical liberal.