Islario general de todas las islas del mundo (General atlas of all the islands in the world) is the greatest work by Seville cosmographer Alonso de Santa Cruz (1505–67). The atlas was begun during the reign of Holy Roman Emperor and King of Spain Charles V and finished in that of his son King Philip II, to whom it was dedicated. It consists of 111 maps representing all the islands and peninsulas of the world, and showing all the discoveries made by European explorers from 1400 to the mid-16th century. The atlas begins with a letter by Santa Cruz to the king, in which he justifies his work and explains different geographic concepts. Preceding the maps is “Breve introducción de la Sphera” in which Santa Cruz makes a cosmographic description, illustrated by 14 astronomical figures. The maps are organized in four parts: the first deals with the North Atlantic; the second, with the Mediterranean and adjacent areas; the third, with Africa and the Indian Ocean; and the fourth with the New World. The maps include scales in latitude and some in longitude and bodies of water with varied scales and oriented with compass roses. The Islario general is the earliest atlas in which paper is used, instead of the parchment that was previously most commonly used for such charts. The design of the maps is more functional, with less attention to aesthetics and more to geographic detail than in the late-medieval portolan maps and atlases. Scholars have determined, on the basis of the dates that appear in the descriptive texts on the islands, that the maps were made beginning in the fourth decade of the 16th century, around 1539, and that the entire atlas was completed circa 1560. It is highly probable that the Islario general was a part of a Geografía Universal that Santa Cruz never finished. Santa Cruz was one of the key figures of the Casa de Contratación (House of Trade) in Seville. One of his first works was a set of the spherical charts of the New World. He created various other works on cosmography and geography, such as the Libro de longitudes; and on historical themes, including Crónica de los Reyes Católicos (Chronicle of the Catholic kings) and Crónica de Carlos V (Chronicle of Charles V). Following Santa Cruz’s death, his successor, Andrés García de Céspedes, attempted to claim credit for this work. On the cover the name Alonso de Santa Cruz has been erased, García de Céspedes’s name is inserted as if he were the author, and the work is dedicated to King Philip III. In the manuscript itself, apocryphal texts have been superimposed over the originals, with the aim of disguising the real authorship and date of creation.