Vlach ( /ˈvlɑːk/ or /ˈvlæk/) is a blanket term covering several modern Latin peoples descending from the Latinised population in Central, Eastern and Southeastern Europe. English variations on the name include: Wallachians, Walla, Wlachs, Wallachs, Vlahs, Olahs or Ulahs. Groups that have historically been called Vlachs include: modern-day Romanians or Daco-Romanians, Aromanians or Macedo-Romanians, Morlachs, Megleno-Romanians and Istro-Romanians. Since the creation of the Romanian state, the term in English has mostly been used for those living outside Romania.

The Vlachs, which would develop into the modern Romanian ethnicity, do not become tangible before the High Middle Ages in Kedrenos (11th century), and their prehistory during the Migration period is a matter of scholarly speculation but according to the linguists and to many scholars, the existence of the present Eastern Romance languages prove the survival of the Thraco-Romans in the low-Danube basin during the Migration period and the Vlachs are all being well considered descendants of Romanised peoples of the area (incl. Thracians, Dacians and Illyrians).

The Vlachs of Serbia (endonym: Rumâni, Serbian: Власи or Vlasi) are an ethnic minority of Serbia, culturally and linguistically related to Romanians. Vlachs mostly live in eastern Serbia, mainly in Timočka Krajina region (roughly corresponding to Bor and Zaječar District districts), but also in Braničevo and Pomoravlje districts. Also a small Vlach population exists in Smederevo and Velika Plana (Podunavlje District), and in the municipalities of Aleksinac and Kruševac (Rasina District), as well as in the South Banat District in Voivodina.

The name they identify with Rumâni din Sârbie in fact means Romanians from Serbia. Although they are ethnographically and linguistically related to the Romanians, within the Vlach community there are divergences on whether they belong or not to the Romanian nation and whether their minority should be amalgamated with the Romanian minority in Vojvodina.

In a Romanian-Yugoslav agreement from the November 4, 2002, the Yugoslav authorities agreed to recognize the Romanian identity of the Vlach population in Central Serbia,^{[dubious – discuss]} but the agreement wasn't applied. In April 2005, 23 deputies from the Council of Europe, representatives from Hungary, Georgia, Lithuania, Romania, Moldova, Estonia, Armenia, Azerbaïdjan, Denmark and Bulgaria protested against Serbia's treatment of this population.