The Island of California refers to a long-held global misconception, dating from the 16th century, that the California region was not part of mainland North America but rather a large island separated from the continent by a strait now known as the Gulf of California.

Garci Rodríguez de Montalvo was a Castilian author who arranged the modern version of the chivalric romance Amadís de Gaula, originally written in three books in the 14th century by an unknown author. Montalvo incorporated a fourth book in the original series, and followed it with a sequel, Las sergas de Esplandián. It is the sequel that Montalvo is most often noted for, mainly because within the book he coined the word California.