About the book (from Wikipedia):
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.”
Mill’s Utilitarianism remains “the most famous defense of the utilitarian view ever written” and is still widely assigned in university ethics courses around the world. Largely owing to Mill, utilitarianism rapidly became the dominant ethical theory in Anglo-American philosophy. Though some contemporary ethicists would not agree with all elements of Mill’s moral philosophy, utilitarianism remains a live option in ethical theory today.