This chapter introduces coins as a key primary source for the study of political, diplomatic, and cultural interaction in the northern frontier region. The coin is not only the most widely and frequently circulated Byzantine object in barbaricum, but also the most reliable and chronologically sensitive. Notwithstanding its own limitations, numismatic material affords the rare opportunity to analyze vast frontier regions in comparison through the lens of a single historical source. This chapter focuses on the Danube and the north-western Black Sea region and demonstrates that Byzantine emperors used money to achieve stability on the frontier by sending gifts of gold coins to various tribal warlords. If gold coins clearly served such political purposes, low-value bronze coins reflect the circulation of common people. Since they are carefully dated with the regnal year of the ruling emperor copper coins confirm the continuous traffic of Byzantine goods across the Danube frontier and highlight the historical conditions responsible for periods of decline or interruption of cultural contact between the two sides of the river.