First published in 1859, John Stuart Mill's On Liberty has exerted an enormous influence on philosophical and political thought ever since. Mill, also famous for his writings on utilitarianism, argues that individual liberty is of paramount importance and that any infringements of it must be kept to an absolute minimum. Mill himself described his brief but brilliant book as asserting 'one very simple principle ... that the sole end for which mankind are warranted, individually or collectively, in interfering in the liberty of any of their number, is self-protection.' Of course, drawing out the implications of this principle has proved to be anything but simple, and the various interpretations of Mill's doctrine have spawned countless debates and mountains of secondary literature. Numerous moral and political theorists have drawn on Mill's work, including Berlin, Rawls and Raz, and his ideas remain as relevant as ever today.