Throughout the long sixth century BCE, family names and conventions for recording them were well established among a restricted segment of the Babylonian urban population. The practice emerged in the eighth and seventh centuries BCE and had antecedents stretching back to the late second millennium. Family names were derived from either ancestral names – typically masculine but occasionally feminine – or occupational titles derived from temple functions. In texts, individuals were designated as descendants of the family name in genealogies that covered two, three, or even four generations. It can be unclear to a modern reader if the final patrilineal ancestor in a genealogy designated a family name or an actual person. This is especially true of two-tier genealogies in which the second tier could be a family name or the father’s name, and the chapter outlines strategies for distinguishing family names in such cases. Family names became common at different times in different parts of Babylonia and some family names were localized to specific locales. The practice can first be observed at Babylon and nearby cities and the spread of some family names was due to the movement of people. The practice never took hold at Nippur.