John Stuart Mill (1806–1873), one of the leading intellectuals of Victorian Britain, is the author of On Liberty. When he published the book in 1859, he had already made his mark on the vital issues of the day with such books as A System of Logic (1843) and The Principles of Political Economy (1848). On Liberty has endured as perhaps his most popular work, principally for its memorable thesis: “The sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection. His own good, either physical or moral, is not a sufficient warrant.” For more than a century and a half, the political arena has been the scene of debate about the question of the extent to which government can and should interfere with the liberty of individuals.