 John Stuart Mill (1806–1873) was the most famous and influential British philosopher of the nineteenth century. He was one of the last systematic philosophers, making significant contributions in logic, metaphysics, epistemology, ethics, political philosophy, and social theory. He was also an important public figure, articulating the liberal platform, pressing for various liberal reforms, and serving in Parliament. During Mill’s lifetime, he was most widely admired for his work in theoretical philosophy and political economy. However, nowadays Mill’s greatest philosophical influence is in moral and political philosophy, especially his articulation and defense of utilitarianism and liberalism (Nicholson 1998). This entry will examine Mill’s contributions to the utilitarian and liberal traditions. We will concentrate on his two most popular and best known works, Utilitarianism (1861, cited as U) and On Liberty (1859, cited as OL), drawing on other texts when this sheds light on his utilitarian and liberal principles. We will conclude by looking at how Mill applies these principles to issues of political and sexual equality in Considerations on Representative Government (1859, cited as CRG), Principles of Political Economy (1848, cited as PPE), and The Subjection of Women (1869, cited as SW).