This Introduction offers a conceptualization of the Indo-Pacific, its islands and their place within the history of science. We argue that Indo-Pacific islands present a remarkable combination of social, political and spatial circumstances, which speak to themes that are central to the history of science. Having driven movements of people and represented staging grounds for explorations, expansions and cross-cultural exchanges, these spaces have been at the forefront of historical change. The historiographies of the two oceans have traditionally emphasized indigenous agency while downplaying European historical trajectories, and therefore they provide historians of science with materials and methodologies that promise nuanced portrayals of knowledge production in cross-cultural settings. Rather than unifying the oceans into a cohesive narrative, we seek to uncover the many horizons of Indo-Pacific worlds and pluralize the spaces within which knowledge travelled at specific times, but not at others. Offering a middle plane between the globe and the region, islands are particularly productive sites for such analyses, as they bring to attention both localized kinds of agency and the impacts of colonialism and globalization. This special issue investigates what happens to knowledge within island spaces and demonstrates that even as small strips of land, islands can significantly enhance our understanding of the practices of knowledge making within the broader contours of world history. In bringing to the fore the contributions of actors from across the wider social spectrum and, especially, the interacting roles of indigenous agents and their traditions, Indo-Pacific worlds thus offer exciting new directions for a field which has often been dominated by a focus on European institutions.