Book excerpt: In this book Christoph Stumpf investigates theological influences upon the legal theory of Hugo Grotius (1583-1645), who is regarded by many as the "father of modern international law". The author analyses how Grotius has contributed to the transformation and further development of international law from its roots in Christian theology to a trans-religious law of nations. From the theological substance in Grotius' views on international relations the author concludes that Grotius' legal theory can be perceived as a theological system of international law.