Four hundred years ago, Hugo Grotius's work De jure belli ac pacis libri tres presented a description of the mutual legal relationship of peoples and states, which is rightly regarded as a milestone in the history of international law. The question of a just war and all subsequent questions are the starting point for this draft of a comprehensive legal system that claims validity without being based on legislation. For centuries, this work by Grotius was a key reference text at universities. This is the first time that a Latin-German edition of Grotius's major work has been published. The extensive sources used by Grotius are documented in a detailed appendix.