Arctic deltas form the critical interface between the Arctic landscape and the ocean. They filter freshwater, sediment, carbon and biochemical fluxes from approximately 14 million km² of northern permafrost terrain. This Review highlights the unique controlling factors, seasonality and morphodynamic processes affecting Arctic deltas. Arctic deltas are ‘ice-dominated systems’ that are affected by land ice, permafrost, and sea ice. They are strongly seasonal and are frozen for 7–9 months of the year. Permafrost limits channel migration. Arctic deltas experience ice jam floods, inducing biochemical exchange with thermokarst lakes. Transport under sea ice creates shallow prodelta ramps. Open-ocean conditions that promote marine reworking of river deposits are short-lived in the Arctic. A data compilation of Arctic deltas highlights that sediment and carbon fluxes are substantially lower than for lower-latitude deltas, with the exception of Greenlandic deltas. Arctic delta morphodynamics are also markedly subdued, with land–water conversion about eightfold less than in low-latitude deltas, probably owing to the unique ice processes occurring in Arctic deltas, which result in preferential floodplain and submarine sedimentation. Future trajectories of controlling factors indicate that Arctic deltas will transition away from being dominated by ice. The open-water season is expanding most rapidly, with wave energy predicted to increase threefold by 2100. Arctic deltas will thaw and experience increased wave influence, with poorly understood consequences for delta morphodynamics and carbon cycling. Process studies under transitional conditions are needed to develop predictive models further.