In the late Middle Ages and the Early Modern period, Northern Europe was a crucible of political, maritime and economic activity. Ships from ports all around the Baltic Sea as well as from the Low Countries plied the Baltic waters, triggering market integration, migration flows, nautical innovations and the dissemination of cultural values. This archival guide is an essential research tool for scholars studying these Baltic connections, providing descriptions of almost 1000 archival collections concerning trade, shipping, merchants, commodities, diplomacy, finances and migration in the years 1450-1800. These rich and varied sources kept at more than 100 repositories in Denmark, Estonia, Finland, Germany, Latvia, Lithuania, the Netherlands, Poland, Russia and Sweden are herewith collected for the first time.