Examen de ingenios para las sciencias (An examination of the talents required for the sciences), first printed in 1575, is the only known work by Juan Huarte de San Juan, who was born in Navarre, Spain, in around 1529. The work seeks to clarify various questions regarding human knowledge and the capacities and abilities found in some persons but not in others, and such questions as what makes a person skilled in one science but not in another and how to recognize which art and science are best suited to each man. It is possible that in writing this work the author was attempting to solve the problem of Spain’s great need in the 16th century for skilled men, especially in government administration and the army, to confront the immense challenges facing the kingdom and its empire. The dedication of the work to King Philip II is one indication of that aim. Some of the chapter titles suggest their contents: “Chapter 6: Which states that the body must be well exercised so that the boy will be skillful;” or “Chapter 11: Wherein it is proved that eloquence and politeness in speech cannot exist in men of great understanding.” The author states that only men have aptitude for sciences, as evidenced by the chapter that explains “What steps must be taken for males to be born, rather than females,” because men are more useful than women. The work was highly successful and underwent several reprints and translations. However, a complaint to the Inquisition forced Huarte to revise the text by removing one chapter and adding others, which resulted in a second revised edition of 1594, presented here. The author died in 1588 and thus did not live to see the reprint, which was completed by his son.