The Vlach law refers to the traditional Romanian common law as well as to various special laws and privileges enjoyed or enforced upon particularly pastoralist communities of Romanian stock or origin in European states of the Late Middle Ages and Early modern period, including in the two Romanian polities of Moldavia and Wallachia, as well as in the Kingdom of Hungary, the Kingdom of Poland, Kingdom of Serbia, the Polish–Lithuanian Commonwealth, etc.

The term Vlachs was initially used in medieval Croatian and Venetian history for a Romance-speaking pastoralist community, called "Vlachs" and "Morlachs", inhabiting the mountains and lands of the Croatian Kingdom and the Republic of Venice from the early 14th century. By the end of the 15th century they were highly assimilated with the Slavs and lost their language or were at least bilingual, while some communities managed to preserve and continue to speak their language (Istro-Romanians).