Any discussion of the function of moral rules in a social environment such as that envisioned by Thomas Hobbes in his “Leviathan” (1651) must first define exactly what is meant by the term “moral rules”. This is because the society or “commonwealth” that Hobbes employs as his theoretical model has no place for morality or moral rules as they are popularly defined. Rather, as this paper will argue, morality in the commonwealth of Hobbes is a product of self-interested humanity. In such an context, as will be seen, the closest analogue to moral rules would be the “civil laws” of the commonwealth which come into being through the “social contract” agreed to by the constituent members of the commonwealth. Finally, the paper will conclude with an analysis of the strengths and weaknesses of Hobbes’ ethical theory.