The Emerald City of Oz is the sixth of L. Frank Baum's fourteen Land of Oz books. Originally published in 1910, it is the story of Dorothy Gale and her Uncle Henry and Aunt Em coming to live in Oz permanently. While Dorothy, Uncle Henry, and Aunt Em are toured through the Quadling Country, the Nome King is assembling allies for an invasion of Oz. The climax takes place in the Emerald City, and the Nome King and his allies are defeated after they drink from the Fountain of Oblivion and forget all their evil plans. Ozma uses the magic belt to send them all home, and to forestall a future invasion of Oz, Glinda uses a magic charm to render Oz invisible and unreachable to everyone except those within the land itself.

Baum had intended to cease writing Oz stories with this book, but financial pressures prompted him to write and publish The Patchwork Girl of Oz, with seven other Oz books to follow.