Complexity theory and network analysis provide a analytical framework to describe social configurations (cities, maritime communities, polities) and environmental phenomena (hydrosphere, climate) as complex systems, entangled via mechanisms of feedbacks, adaptation or disruption. In this volume, this approach is applied on various phenomena of maritime history as discussed within the DFG-funded Special Research Programme (SPP 1630) »Harbours from the Roman Period to the Middle Ages« (www.spp-haefen.de).