The Principle of Fairness and Natural Duties defends the Principle of Fairness (PoF) as a widely applicable moral principle that can ground obligations to obey the law. The first three chapters develop an interpretation of the PoF by responding to criticisms from A. John Simmons. Simmons argues that, for the principle of fairness to generate obligations, beneficiaries of cooperative public-goods schemes must voluntarily accept the benefits they receive. I argue against Simmons’s voluntarism by showing that, even on his view, mere receipt of benefits that are worth their cost can trigger fairness obligations. In a similar vein, Simmons argues that the PoF requires a type of cooperation that we do not see in political communities. Thus, even ...