The Natural History (Latin: Naturalis historia) is a Latin work by Pliny the Elder. The largest single work to have survived from the Roman Empire to the modern day, the Natural History compiles information gleaned from other ancient authors. Despite the work's title, its subject area is not limited to what is today understood by natural history; Pliny himself defines his scope as "the natural world, or life". It is encyclopaedic in scope, but its structure is not like that of a modern encyclopaedia. It is the only work by Pliny to have survived, and the last that he published. He published the first 10 books in AD 77, but had not made a final revision of the remainder at the time of his death during the AD 79 eruption of Vesuvius. The rest was published posthumously by Pliny's nephew, Pliny the Younger.

The work is divided into 37 books, organised into 10 volumes. These cover topics including astronomy, mathematics, geography, ethnography, anthropology, human physiology, zoology, botany, agriculture, horticulture, pharmacology, mining, mineralogy, sculpture, art, and precious stones.

Pliny's Natural History became a model for later encyclopaedias and scholarly works as a result of its breadth of subject matter, its referencing of original authors, and its index.

Pliny's Natural History was written alongside other substantial works (which have since been lost). Pliny (AD 23–79) combined his scholarly activities with a busy career as an imperial administrator for the emperor Vespasian. Much of his writing was done at night; daytime hours were spent working for the emperor, as he explains in the dedicatory preface addressed to Vespasian's elder son, the future emperor Titus, with whom he had served in the army (and to whom the work is dedicated). As for the nocturnal hours spent writing, these were seen not as a loss of sleep but as an addition to life, for as he states in the preface, Vita vigilia est, "to be alive is to be watchful", in a military metaphor of a sentry keeping watch in the night. Pliny claims to be the only Roman ever to have undertaken such a work, in his prayer for the blessing of the universal mother:

Hail to thee, Nature, thou parent of all things! and do thou deign to show thy favour unto me, who, alone of all the citizens of Rome, have, in thy every department, thus made known thy praise.

The Natural History is encyclopaedic in scope, but its format is unlike a modern encyclopaedia. However, it does have structure: Pliny uses Aristotle's division of nature (animal, vegetable, mineral) to recreate the natural world in literary form. Rather than presenting compartmentalised, stand-alone entries arranged alphabetically, Pliny's ordered natural landscape is a coherent whole, offering the reader a guided tour: "a brief excursion under our direction among the whole of the works of nature ..." The work is unified but varied: "My subject is the world of nature ... or in other words, life," he tells Titus.

Nature for Pliny was divine, a pantheistic concept inspired by the Stoic philosophy, which underlies much of his thought, but the deity in question was a goddess whose main purpose was to serve the human race: "nature, that is life" is human life in a natural landscape. After an initial survey of cosmology and geography, Pliny starts his treatment of animals with the human race, "for whose sake great Nature appears to have created all other things". This teleological view of nature was common in antiquity and is crucial to the understanding of the Natural History. The components of nature are not just described in and for themselves, but also with a view to their role in human life. Pliny devotes a number of the books to plants, with a focus on their medicinal value; the books on minerals include descriptions of their uses in architecture, sculpture, art, and jewellery. Pliny's premise is distinct from modern ecological theories, reflecting the prevailing sentiment of his time.

Pliny's work frequently reflects Rome's imperial expansion, which brought new and exciting things to the capital: exotic eastern spices, strange animals to be put on display or herded into the arena, even the alleged phoenix sent to the emperor Claudius in AD 47 – although, as Pliny admits, this was generally acknowledged to be a fake. Pliny repeated Aristotle's maxim that Africa was always producing something new. Nature's variety and versatility were claimed to be infinite: "When I have observed nature she has always induced me to deem no statement about her incredible." This led Pliny to recount rumours of strange peoples on the edges of the world. These monstrous races – the Cynocephali or Dog-Heads, the Sciapodae, whose single foot could act as a sunshade, the mouthless Astomi, who lived on scents – were not strictly new. They had been mentioned in the fifth century BC by Greek historian Herodotus (whose history was a broad mixture of myths, legends, and facts), but Pliny made them better known.