Polar Regions directly influence the whole Earth system. They play a major role in global ocean circulation, with both regions being sources of deep and bottom waters and strong wind and buoyancy-forcing in the Southern Ocean driving much of the circulation. Arctic sea ice is declining rapidly, and the climatological and ecological impacts of an ice-free Arctic are unknown. The Southern Ocean is also a major oceanic sink for CO2. Polar change therefore has global consequences. Changes in Arctic sea ice will affect the productive marginal shelf seas first, with both ice thickness and seasonal duration predicted to decrease significantly in the coming decades. Seasonal shifts in ice patterns may result in increasing mismatches between primary productivity and larval recruitment. The surface waters around parts of Antarctica are already warming and the Southern Ocean is becoming less effective as a major carbon sink. Increasing ocean acidification will impact at the Poles first, with a range of calcifying and non-calcifying species becoming threatened. Increasing temperatures will place stress on the largely stenothermic invertebrate fauna. The biogeochemical function of Polar Regions, as well as controlling factors such as iron limitation, is being increasingly revealed. The nature of large scale drivers of inter-annual variability, such as ENSO and the NAO, are also becoming further appreciated. This multidisciplinary session invites papers focussing on the importance, structure and sensitivity of the Polar Regions, from physical, biogeochemical and ecological perspectives. This includes insights gained from field observations, remote sensing and modelling.