Hedonism is a materialist and atheist philosophy which emphasizes the pursuit of personal pleasure above all other considerations, or as the sole consideration in life.
Hedonism, in everyday usage of the word, is the mindless surrender to the pleasure of the moment. An individual is called hedonistic if he gives in to feelings, lusts, and appetites. Various philosophical schools construct a more sophisticated system based on a “hedonic calculus” that attempts to avoid "the road to perdition" that surely results from the mindless pursuit of pleasure. Since immediate pleasure is felt more intensely than uncertain pain in the distant future, such attempts stand on weak ground.
The classical attempt to ground ethics in a system of pleasure is Epicureanism. The cowardly withdrawal from the challenges and duties of civic life led Cicero to disparage Epicurianism above all other classical schools. Cicero's critique of this materialist and essentially atheist creed was absorbed by Christian philosophers.
John Locke presented a superior attempt at a “hedonic calculus” in his “Essay Concerning Human Understanding.” Interestingly enough, he held that the fear of consequences in the afterlife were important to make the calculations work. Thomas Jefferson held this view.
A full utilitarian hedonic philosophical system emerged with Jeremy Bentham, the father of Utilitarianism. However, the pleasure one maximizes isn't one's own but society's. One actually deprives oneself of pleasure if society's aggregate pleasure is increased. Bentham denigrated natural rights as he advocated collective pleasure, "the greatest good for the greatest number." This paved the way for modern collectivism where the individual's property and life can be disposed of as the whim of the people (in practice the state) determines.
Bentham's specific policies remained respectable as did his pupil, John Stuart Mill. Mill's "On Liberty" remains a classic in classical liberal thought. The failure of utilitarianism as a foundation is evident as Mill ended his life as a socialist. While a few libertarians main a defense of liberty on pure utilitarian grounds, utilitarian thought generally leads to socialism for the simple reason that immediate pleasure is more certain that abstract calculations. Politicians who promise free goods to the electorate easily buy votes in a more hedonistic oriented culture.