The Cyrenaics or Kyrenaics, were a sensual hedonist Greek school of philosophy founded in the 4th century BCE, supposedly by Aristippus of Cyrene, although many of the principles of the school are believed to have been formalized by his grandson of the same name, Aristippus the Younger. The school was so called after Cyrene, the birthplace of Aristippus. It was one of the earliest Socratic schools. The Cyrenaics taught that the only intrinsic good is pleasure, which meant not just the absence of pain, but positively enjoyable sensations. Of these, momentary pleasures, especially physical ones, are stronger than those of anticipation or memory. Further, they recognized the value of social obligation and that pleasure could be gained from altruistic behaviour. The school died out within a century and was replaced by the philosophy of Epicureanism.

Aristippus of Cyrene was a hedonistic Greek philosopher and the founder of the Cyrenaic school of philosophy. He was a pupil of Socrates, but adopted a different philosophical outlook, teaching that the goal of life was to seek pleasure by adapting circumstances to oneself and by maintaining proper control over both adversity and prosperity. His view that pleasure is the only good came to be called ethical hedonism. Due to the ideological and philosophical differences between Socrates and himself, Aristippus faced backlash by Socrates and many of his fellow-pupils. Out of his hedonistic beliefs, Aristippus' most famous phrase was, "I possess, I am not possessed." Despite having two sons, Aristippus identified his daughter Arete as the "intellectual heiress" of his work, resulting in the systematization of his work and the Cyrenaic school of philosophy, by Arete, and her son Aristippus the Younger, Aristippus' grandson, during the later years of his life and after his death.