Merlyn, knowing the boy's destiny, teaches Arthur (known as "Wart") what it means to be a good king by turning him into various kinds of animals: fish, hawk, ant, goose, and badger.

While the young king suppresses initial rebellions, Merlyn leads him to envision a means of harnessing potentially destructive Might for the cause of Right: the chivalric order of the Round Table.

Floyd C. Gale praised The Sword in the Stone as "blithely comic and entirely delightful", stating that it was "in utter contrast to the mounting tragedy" of the other three volumes of the series.

"[4] Constance Grady of Vox also praised the novel, stating: "White was writing for a post–World War II audience, but his book has a vigor and clarity that makes it an urgent and important read today.

Alan Jay Lerner and Frederick Loewe's 1960 musical Camelot (which was made into a movie in 1967) is based mostly on the last two books of The Once and Future King and features White's idea of having Thomas Malory make a cameo appearance at the end, again as "Tom of Warwick".

BBC Radio 4 serialised the book in six one-hour episodes dramatised by Brian Sibley, beginning on Sunday 9 November 2014 with Paul Ready as Arthur and David Warner as Merlyn.