On the Nature of Things (or De Rerum Natura in the original Latin) is a philosophical poem written by the Epicurean Lucretius (ca 99-55 BCE). The poem is divided into six 'books' or sections and each of these books deals with different aspects of Epicurean thought. In order to summarize On the Nature of Things, I will offer a brief summary of each of the books.

Book I: Lucretius begins by defending science against superstition in the first four hundred lines. After this, he describes and defends atomic theory: like the pre-Socratics Democritus and Leucippus and like the earlier Epicureans, Lucretius defends a view of the physical universe according to which all that exists are atoms and void. This materialist explanation was highly heterodox in antiquity and was ridiculed by other philosophical schools (Academics, Peripatetics, Stoics). Book I concludes with a consideration of the composition of physical bodies; this spills over into Book II. The conclusion of this discussion is that space and time are infinite.

Book II: After finishing his discussion of the composition of physical bodies, Lucretius discusses the highly controversial idea of atomic swerve. He holds that the atoms that make up the universe have a character and a will of their own and their motion is not uniform and linear but that they may, from time to time, choose to swerve.

Book III: He begins again by praising Epicurus for revealing the truth about the nature of things and discusses some key aspects of Epicurean ethical doctrine. He describes the Epicurean 'tetrapharmakon' (four-fold remedy): one must not fear death, what is good is easy to get, what is difficult is easy to survive, and one must not fear the gods. We also learn that the body and soul are material and mortal and that this belief is the metaphysical basis for the tetrapharmakon.

Book IV: This is given over entirely to a discussion of sex. The model of sex proposed is an androcentric, hydraulic model. He recognizes that women and men both gain pleasure from sex and also counsels promiscuity.

Book V: Book V is mostly given over to his cosmological doctrines. One of the central claims is that the world is not created by a divine intellect nor by gods. Further, the world is not eternal but mortal. After this discussion, he introduces what might well be the earliest (Western) version of a social contract theory according to which people decided to live together in societies because of a compact. He ends Book V with a discussion of pleasure and hedonism.

Book VI: In the final book, Lucretius talks about celestial phenomena at first. Then he talks about disease and health, with a focus on the Athenian plague.