A phylarch (Greek: φύλαρχος, Latin: phylarchus) is a Greek title meaning "ruler of a tribe", from phyle, "tribe" + archein "to rule".

In Classical Athens, a phylarch was the elected commander of the cavalry provided by each of the city's ten tribes.

During the Hellenistic period, the term had its literal meaning as head of a tribe. It seemed to apply to Arabs who commanded tribes, essentially the equivalent to "sheikh".^[1] This usage continued in the later Roman Empire of the 4th to 7th centuries, where the title was given to the leading princes of the Empire's Arab allies in the East, both those settled within the Empire and outside. From ca. 530 to ca. 585, the individual phylarchs were subordinated to a supreme phylarch from the Ghassanid dynasty.^[2]

In Thomas More's Utopia (1516), leaders of Utopian cities are called phylarchs.^[3]