After a brief discussion of prehistory and pre-Roman and Roman past of the territory of modern Serbia, the chapter turns to the Slav and Avar migrations of the sixth and seventh centuries, which permanently altered the demographics of Central and South-Eastern Europe. It then explores the origins of the Serbs and traces the formation of the first Serb and South Slav polities in the ninth and tenth centuries. Key to understanding this period is the Serbs’s relationship with Byzantium and neighbouring peoples, including Bulgarians, Croats and Hungarians. The chapter also explores the Serbs’ conversion to Christianity and the beginning of literacy among the South Slavs.