The Water-Babies: A Fairy Tale for a Land-Baby is a children's novel by Charles Kingsley. Written in 1862–1863 as a serial for Macmillan's Magazine, it was first published in its entirety in 1863. It was written as part satire in support of Charles Darwin's On the Origin of Species. The book was extremely popular in the United Kingdom and was a mainstay of British children's literature for many decades. The book was selected by Julia Eccleshare as one of the 1001 Children's Books You Must Read Before You Grow Up (2009).

The protagonist is Tom, a young chimney sweep, who falls into a river after encountering an upper-class girl named Ellie and being chased out of her house. There he appears to drown and is transformed into a "water-baby", as he is told by a caddisfly – an insect that sheds its skin – and begins his moral education. The story is thematically concerned with Christian redemption, though Kingsley also uses the book to argue that England treats its poor badly, and to question child labour, among other themes.

Tom embarks on a series of adventures and lessons, and enjoys the community of other water-babies on Saint Brendan's Island once he proves himself a moral creature. The major spiritual leaders in his new world are the fairies Mrs. Doasyouwouldbedoneby (a reference to the Golden Rule), Mrs. Bedonebyasyoudid, and Mother Carey. Weekly, Tom is allowed the company of Ellie, who became a water-baby after he did.

Grimes, his old master, drowns as well, and in his final adventure, Tom travels to the end of the world to attempt to help the man where he is being punished for his misdeeds. Tom helps Grimes to find repentance, and Grimes will be given a second chance if he can successfully perform a final penance. By proving his willingness to do things he does not like, if they are the right things to do, Tom earns himself a return to human form, and becomes "a great man of science" who "can plan railways, and steam-engines, and electric telegraphs, and rifled guns, and so forth". He and Ellie are united, although the book states (perhaps jokingly) that they never marry, claiming that in fairy tales, no one beneath the rank of prince and princess ever marries.

The book ends with the caveat that it is only a fairy tale, and the reader is to believe none of it, "even if it is true".

In the style of Victorian-era novels, The Water-Babies is a didactic moral fable. In it, Kingsley expresses many of the common prejudices of that time period, and the book includes dismissive or insulting references to Americans, Jews, Blacks, and Catholics, particularly the Irish.

The book had been intended in part as a satire, a tract against child labour, as well as a serious critique of the closed-minded approaches of many scientists of the day in their response to Charles Darwin's ideas on evolution, which Kingsley had been one of the first to praise. He had been sent an advance review copy of On the Origin of Species, and wrote in his response of 18 November 1859 (four days before Darwin's book was published) that he had "long since, from watching the crossing of domesticated animals and plants, learnt to disbelieve the dogma of the permanence of species," and had "gradually learnt to see that it is just as noble a conception of Deity, to believe that He created primal forms capable of self development into all forms needful pro tempore and pro loco, as to believe that He required a fresh act of intervention to supply the lacunas which He Himself had made", asking "whether the former be not the loftier thought."

In the book, for example, Kingsley argues that no person is qualified to say that something that they have never seen (like a human soul or a water-baby) does not exist.