Italian jurist considered by many to be the founder of the science of international law and said to have been the first in western Europe to separate secular law from Roman Catholic theology and canon law.

A graduate of the University of Perugia, Italy (doctor of civil law, 1572), Gentili was exiled from Italy in 1579 because of his Protestantism. From 1581 until his death he taught at the University of Oxford, becoming well known for his lectures on Roman law and for his numerous writings.

In 1588 Gentili published De jure belli commentatio prima (“First Commentary on the Law of War”), the first of a three-volume series. A complete, revised edition appeared in 1598 as De jure belli libri tres (Three Books on the Law of War). In his view, international law should comprise the actual practices of civilized nations, tempered by moral (but not specifically religious) considerations. Although he rejected the authority of the church, he used the reasoning of the canon law as well as the civil law whenever it suited his purpose. The Dutch jurist Hugo Grotius (Grotius, Hugo), in writing the much better known De Jure Belli ac Pacis (1625; On the Law of War and Peace), drew extensively on Gentili's work.