This essay examines the development of the major themes in the natural law account of property, and of the conceptions of social life and moral action on which they rely, from Hugo Grotius to David Hume. In the opening two chapters, the two main variants of modern n a tu ra l law theory, those of Grotius and Pufendorf, are explained in some detail. Their understanding of natural law, as a science of morals grounded in human nature, is spelled out, and it is shown how this results in an understanding of property relations as a natural response to the changes in human circumstances wrought by increasing sophistication in human social life. It is a natural response because it reflects the requirements of human nature, such reflection being shown by the fact th a t it arises necessarily, through peaceful processes, from the recognition of the elemental moral realm of what is “one’s own” . In this sense property has a natural history; but it is also shown th a t, for these theories, the division between natural history and actual history is not sufficiently clearly drawn, an inadequacy which is well illustrated by problems in the account of the place of slavery in the account of property. But Pufendorf, at least, recognizes th a t the problem of slavery can be reduced if the principal incentive to voluntary enslavement, material necessity, can itself be overcome. In this way the problem of slavery can have an economic solution. By carefully examining the implications of the basic notion of “one’s own” , which, following English practice, he calls property in one’s person, Locke concludes both that slavery is always unacceptable (is unnatural) and th a t the origin of property in no way depends on consent. Rather, property is shown to be the inevitable consequence of human self-preserving action in a world given to us by God. Neither does material necessity provide a reason for enslavement: on the one hand, the right of charity of the poor against the surplus of the wealthy makes enslavement an avoidable option for the individual; and on the other, the productive power of improving labour is so great th a t, where a system of private property is established which secures the fruits of their industry to the industrious, necessity itself (and thereby slavery also) becomes avoidable for a whole society, by making even the worst off wealthier than the richest in a primitive economy. Thus the question of property undergoes a significant shift. The concern of Locke’s successors with political economy, and the manner in which this concern modifies their interest in slavery and necessity as serious problems for society shows the extent to which Locke’s conclusions win the day. The question of what it is to have a social theory which is grounded in human nature becomes very pressing, however, because of difficulties perceived to be generated by Lockean (and, more generally, all “self-love” ) theories of human motivation. Such theories were perceived as compromising the natural law stress on the naturalness of human social life. The issue hinges on the nature of obligation. Hutcheson (and, following him, Hume) defends an account of human motivation which allocates a central role to impartial benevolence, and which thereby offers an understanding of moral obligation independent of theological commitments. Hutcheson’s programme runs into difficulties in its account of property, however, stressing the necessity of strict rule-following while at the same time providing general principles which threaten it. Hume’s account of the source of our obligation to respect the rules of property (the cornerstone of justice) is explained as an attempt to overcome this tension, by adapting some Pufendorfian distinctions to account for different types of moral obligation, grounded in different aspects of human sociability. So, despite some well established assumptions to the contrary, Hume can be recognized to be an important contributor to the natural law tradition. Together, he and Hutcheson pave the way for the more complete critical natural history of Adam Smith.