De jure belli ac pacis (On the Law of War and Peace) is a 1625 book in Latin, written by Hugo Grotius and published in Paris, on the legal status of war. It is now regarded as a foundational work in international law.
Its content owed much to Spanish theologians of the previous century, particularly Francisco de Vitoria and Francisco Suarez, working in the Catholic tradition of natural law.
Grotius began writing the work while in prison in the Netherlands. He completed it in 1623, at Senlis, in the company of Dirck Graswinckel.
According to Pieter Geyl:
“ It is an attempt by a theologically and classically educated jurist to base upon law order and security in the community of states as well as in the national society in which he had grown up. In the rather naïve rationalism, the belief in reason as the lord of life, is revealed the spiritual son of Erasmus.