Stephen of Byzantium was a Byzantine grammarian and lexicographer active during the reign of Emperor Justinian I in the sixth century CE. While precise biographical details are lost, his scholarship indicates he was a highly educated figure, likely working in Constantinople. His career belongs to the period of encyclopedic compilation characteristic of the early Byzantine era.

His monumental work is the Ethnika, a geographical lexicon describing cities, peoples, and places from the known world, including their historical, mythological, and ethnographic details. The original text is lost but survives through an epitome by Hermolaus and numerous fragments preserved in later Byzantine lexica and commentaries.

The Ethnika was a work of immense erudition and became a fundamental reference for Byzantine scholarship. It preserved vast amounts of geographical and historical information from earlier Greek literature and served as a crucial source for later lexicographers, geographers, and commentators throughout the medieval period. It remains a primary source for studying ancient Greek geography and the reception of classical knowledge in Late Antiquity.