The idea of just war, which even denied the admissibility of a military attack as a way to resolve disputes at all, derives from the earliest times of humanity and both are nearly as old as the war itself. Not to mention the famous words from ‘The Book of Isaiah’ about beating the swords into ploughshares, a great deal of doctrines, most of them similar, appeared throughout the ages. One of them was the one introduced by a fifteenth century Polish scholar, Stanislas of Scarbimiria, in his ‘Sermon on just wars’. This first codification of a body of public international law based on a professional scientific research, objectively deals with a great deal of problems regarding the justified declaring war and of wartime conduct. Both in his way of writing and his approach to examined matters, Stanislas seemed to be much closer to the modern points of view on the law of war, unlike his contemporaries.