Cultural interactions between Aboriginal peoples of northeastern Australia and Melanesian peoples of southern New Guinea have caught the attention of anthropologists and archaeologists since the nineteenth century. Moving away from older models of one-way diffusion of so-called advanced cultural traits from New Guinea to mainland Australia via Torres Strait, this article elaborates the concept of the Coral Sea Cultural Interaction Sphere (CSCIS) as a framework to investigate two-way interactions, gene flow, and object movements across Torres Strait. The CSCIS centres on a series of ethnographically known, canoe-voyaging, and long-distance maritime exchange networks that linked communities over a distance of 2000 km along the south coast of mainland Papua New Guinea and the northeast coast of Australia. Archaeological evidence for temporal changes in the geographical spread of pottery and obsidian use indicates that the CSCIS was historically dynamic, with numerous reconfigurations over the past 3000 years. The CSCIS developed as the confluence of major cultural changes and demographic expansions that took place in northeastern Australia and southern mainland Papua New Guinea.