John Stuart Mill's book Utilitarianism is a classic exposition and defence of utilitarianism in ethics. The essay first appeared as a series of three articles published in Fraser's Magazine in 1861; the articles were collected and reprinted as a single book in 1863.

Mill's aim in the book is to explain what utilitarianism is, to show why it is the best theory of ethics, and to defend it against a wide range of criticisms and misunderstandings. Though heavily criticized both in Mill's lifetime and in the years since, Utilitarianism did a great deal to popularize utilitarian ethics and has been considered "the most influential philosophical articulation of a liberal humanistic morality that was produced in the nineteenth century."

John Stuart Mill (20 May 1806 – 7 May 1873), usually cited as J. S. Mill, was a British philosopher, political economist, and civil servant. One of the most influential thinkers in the history of classical liberalism, he contributed widely to social theory, political theory, and political economy. Dubbed "the most influential English-speaking philosopher of the nineteenth century", Mill's conception of liberty justified the freedom of the individual in opposition to unlimited state and social control.