During the Middle Ages and early modern period the French kings and their vassals constantly asserted the importance and, in effect, primacy of customary law, especially in the lands north and west of Paris. The area where the French customary law (droit coutumier) was in force was known as the pays de coutume. In the south of France Roman law was paramount (pays de droit écrit). The line separating the two areas was generally the river Loire, from Geneva to the mouth of the Charente.
A number of regional coutumes were compiled in the 13th and 14th centuries. The Coutumes de Beauvaisis, compiled by Phillipe de Remy, had a long-lasting influence on French law. There were about 60 such regional coutumes. There were also more than 300 coutumes locales in specific towns and villages. Voltaire said that in France a traveler changed laws as often as he changed horses.
However, by the 16th century the Coutumes of Paris (first published in 1510) had been adopted in all areas except Normandy, Burgundy and Brittany. Further development of customary law had been halted by the late 16th century.
In 1664 under the royal Act creating the French East India Company the Coutumes of Paris became the only legal code in New France. In 1866 the Civil Code of Lower Canada was adopted in Lower Canada. The majority of the Code's rules derived from the Coutumes of Paris.