De jure belli ac pacis

De iure belli ac pacis (English: On the Law of War and Peace) is a 1625 work by Dutch jurist and philosopher Hugo Grotius, which is widely regarded as a foundational text in the development of international law. First published in Paris, the work sets out to establish a legal framework for war and peace based on natural law, reason, and customary norms among nations (jus gentium).

Several editions of the work appeared during Grotius’s lifetime; the final, published in Amsterdam in 1646, is widely regarded by scholars as the version most faithful to his authorial intentions, reflecting his mature legal and philosophical views.

De iure belli ac pacis enjoyed enduring influence and widespread circulation across Europe. It was reprinted in numerous editions—over 70 identified in major bibliographies, including translations into several European languages—demonstrating its importance across confessional and national boundaries. The work remained a central reference in the study of law and political theory, taught in academic institutions for centuries, and continues to be cited in debates surrounding just war theory, state sovereignty, and the principles of international law.

The work builds upon earlier ideas, particularly those of Alberico Gentili in De iure belli of 1598 as demonstrated by Thomas Erskine Holland and was influenced by Spanish scholastics such as Francisco de Vitoria and Francisco Suárez. Grotius composed much of the text while imprisoned in the Netherlands and completed it in 1623 at Senlis, with the assistance of Dirck Graswinckel.