This special issue uses information as a lens through which to examine the operation of the Renaissance world’s composite polities and political unions, such as the Venetian thalassocracy or the Spanish Empire. To date, late-medieval and early modern scholarship has mostly neglected the role of information in ruling those polities. Yet information was crucial, for it allowed authorities to know what was happening in their dominions and colonies and thus shaped their policies and interactions with local political societies. The authors of this special issue suggest that a focus on information can help us fully understand how composite polities operated, whether on a regional, Mediterranean or global scale. This introductory essay examines the historiographical debate about late-medieval and early modern composite polities and unions and discusses how and to what extent communication strategies, record-keeping practices and data accumulation can be used to understand how authorities relied on information to exercise their rule over their various dominions. It also discusses this approach in relation to this special issue’s six case studies and other examples of pre-modern composite polities.