Nicolas Camille Flammarion FRAS (French: [nikɔla kamij flamaʁjɔ̃]; 26 February 1842 – 3 June 1925) was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and works on psychical research and related topics. He also published the magazine L'Astronomie, starting in 1882. He maintained a private observatory at Juvisy-sur-Orge, France.

Camille Flammarion was born in Montigny-le-Roi, Haute-Marne, France. He was the brother of Ernest Flammarion (1846–1936), the founder of the Groupe Flammarion publishing house. In 1858, he became a professional at computery at the Paris Observatory. He was a founder and the first president of the Société astronomique de France, which originally had its own independent journal, BSAF (Bulletin de la Société astronomique de France), which was first published in 1887. In January 1895, after 13 volumes of L'Astronomie and 8 of BSAF, the two merged, making L’Astronomie its bulletin. The 1895 volume of the combined journal was numbered 9, to preserve the BSAF volume numbering, but this had the consequence that volumes 9 to 13 of L'Astronomie can each refer to two different publications five years apart.

The "Flammarion engraving" first appeared in Flammarion's 1888 edition of L’Atmosphère. In 1907, he wrote that he believed that dwellers on Mars had tried to communicate with Earth in the past. He also believed in 1907 that a seven-tailed comet was heading toward Earth. In 1910, for the appearance of Halley's Comet, he was widely but falsely reported as believing the gas from the comet's tail "would impregnate [the Earth’s] atmosphere and possibly snuff out all life on the planet".

As a young man, Flammarion was exposed to two significant social movements in the western world: the thoughts and ideas of Darwin and Lamarck and the rising popularity of spiritism with spiritualist churches and organizations appearing all over Europe. He has been described as an "astronomer, mystic, and storyteller" who was "obsessed by life after death, and on other worlds, and [who] seemed to see no distinction between the two".

He was influenced by Jean Reynaud (1806–1863) and his Terre et ciel (1854), which described a religious system based on the transmigration of souls believed to be reconcilable with both Christianity and pluralism. He was convinced that souls after the physical death pass from planet to planet and progressively improve at each new incarnation. In 1862, he published his first book, The Plurality of Inhabited Worlds, and was dismissed from his position at the Paris Observatory later the same year. It is not quite clear if these two incidents are related to each other.

In Real and Imaginary Worlds (1864) and Lumen (1887), he "describes a range of exotic species, including sentient plants which combine the processes of digestion and respiration. This belief in extraterrestrial life, Flammarion combined with a religious conviction derived, not from the Catholic faith upon which he had been raised, but from the writings of Jean Reynaud and their emphasis upon the transmigration of souls. Man he considered to be a “citizen of the sky,” other worlds “studios of human work, schools where the expanding soul progressively learns and develops, assimilating gradually the knowledge to which its aspirations tend, approaching thus evermore the end of its destiny.”

His psychical studies also influenced some of his science fiction, where he would write about his beliefs in a cosmic version of metempsychosis. In Lumen, a human character meets the soul of an alien, able to cross the universe faster than light, that has been reincarnated on many different worlds, each with its own gallery of organisms and their evolutionary history. Other than that, his writing about other worlds adhered fairly closely to then current ideas in evolutionary theory and astronomy. Among other things, he believed that all planets went through more or less the same stages of development, but at different rates depending on their sizes.

The fusion of science, science fiction and the spiritual influenced other readers as well; "With great commercial success he blended scientific speculation with science fiction to propagate modern myths such as the notion that “superior” extraterrestrial species reside on numerous planets, and that the human soul evolves through cosmic reincarnation. Flammarion's influence was great, not just on the popular thought of his day, but also on later writers with similar interests and convictions." In the English translation of Lumen, Brian Stableford argues that both Olaf Stapledon and William Hope Hodgson have likely been influenced by Flammarion. Arthur Conan Doyle's The Poison Belt, published 1913, also has a lot in common with Flammarion's supposed worries that the tail of Halley's Comet would be poisonous for earth life. Edgar Rice Burroughs makes a direct reference to Flammarion in Skeleton Men of Jupiter.