Maritime exchange and its social dimensions substantially define global relationships in our modern world. Archaeology as a discipline has a long history investigating exchange and this research has been used to understand the extent of spheres of interactions between distant communities, risk minimisation strategies of communities living in unpredictable environments, advances in technology, cultural diversification, and emergence of social hierarchies and inequalities. Obsidian and the Sea elucidates the long-lasting human relationship with the sea, demonstrating the crucial role of the coast and open waters alike in the development of prehistoric coastal communities, human migration trajectories and island settlement in deep time. This book’s novel approach is to focus on one material in particular, obsidian, to explore how it reveals the use of the sea in prehistory across different times and places. The case studies presented here demonstrate especially well that, throughout history and across different regions, humans have engaged with obsidian exchange not solely as an economic activity, but, significantly, in a symbolic way to denote social connectivity at great distances and oftentimes in absentia, meaning without the need for face-to-face interactions. Obsidian’s unique physical attributes – brilliance, iridescence, transparency, colour – are an integral part of the human condition and have a strong emotional impact to its consumers. They facilitated the maintenance of mental maps of preferential routes and desired social networks diachronically with the sea functioning as a highway for communication.