The story of King Canute (Cnut) is well known. Indeed, in perhaps its most familiar form it exists as an oral historical tradition passed from generation to generation. In this almost legendary account, King Canute is depicted as an arrogant ruler, so confident as to his own omnipotence that he takes on the forces of nature, pitting his own powers against those of the rising tide – his wet robes paying testament to his powerlessness in the face of potent material forces and to the triumph of (natural) structures over (human) agency. Or so it might seem. In this article I suggest that even in this, the simplest depiction of the story of Canute, the relationship between structure and agency is more complex and involved than it appears. This complexity is only accentuated if we turn from the legend to the historical evidence. Moreover, by reflecting on Canute's practical negotiation of the ‘problem’ of structure and agency we can not only gain an interesting political analytical purchase on a seemingly familiar tale, but we can also generate a series of valuable and more general insights into our understanding of the structure–agency relationship. In particular, the (various) stories of King Canute and the waves alert us to the need: (1) to maintain a clear distinction between the empirical and the ontological; (2) to resist the temptation to attempt an empirical adjudication of ontological issues (or, indeed, an ontological adjudication of empirical issues); (3) to differentiate clearly between the capacities of agents with respect to material/physical structures on the one hand, and social/political structures on the other; (4) to acknowledge the significance of unintended consequences; (5) to attend to the ‘performative’ dimensions of agency; and (6) to recognise the dangers inherent in an overly instrumental view of actors' motivations and intentions.