The article is devoted to the research of life and work of a well-known French scientist of the XVI century Charles Dumoulin, the founder of the theory of an autonomy of will in the international private law. Dumoulin, as all his predecessors, proceeded from sustantive law norms. Innovation of the scientist is an idea about the right of the parties freely to choose an applicable law not only by means of the special agreement, but also according to their silent or even the hypothetical agreement. The scientist managed to spell out his own doctrine of conflict of laws:in contractual relations when conflict of laws occurs the law chosen by the parties prevails.