The subject matter of the paper is the theory of international private law developed in a treatise of theGerman 17th century scholar Johann Nikolaus Hert. The paper examines the major doctrines, rulesof resolving conflicts of laws, their significance and topicality for the modern international private law.The personality of Johann Nikolaus Hert locates the central place in the German statutory theory.The ways of resolving conflicts of the laws belonging to different nations, proposed by this scholardetermined the development of German conflict of law doctrines of the 19th and 20th centuries; thepractical solutions developed by him are fixed in the modern legislation and case practice. However,Hert’s conflict of laws theory is controversial, ambiguous, real examples do not fit the rigid theoreticalcategories. The paper concludes that with all the criticism of Hert’s theory, he contributed significantly tothe development of the international private law doctrine. He developed the terminology of internationalprivate law and enriched it with terms collisions of laws, conflict of laws embraced by legal practice,legislation and doctrine in the majority of countries. Hert’s three rules are in essence three variants offoreign element (subject, object, fact) which are to be found and assessed in terms of the choice of acompetent legislation. His 63 cases cover the law of persons, inheritance, property rights of spouses,contracts, process, i.e. all spheres prone to conflict of laws. Hert’s dissertation featured completely allthe potential conflict of law situations. He confirmed the classical interpretation of mixed statutes as thelaws on the form of legal actions; insisted on the obligation to apply foreign law, pointed to the necessityto unify local laws to avoid interlocal collisions. All these results are of high significance and though inhis theory «Hert is a victim of different, sometimes incompatible influences”, his practical tactfulnessalways helped him to find proper solutions during conflict of laws.