We observe and quantify the modern and past state of terrestrial and submarine permafrost and predict its future transformation in a changing climate. We measure long-term hydroclimate and ground temperatures, study water and energy balance, use remote sensing to quantify thaw, and model past, current, and future permafrost. We employ geophysics, quantify fluxes from permafrost thaw and coastal erosion, and determine greenhouse gas and biogeochemical fluxes. We reconstruct periglacial landscape dynamics over the past 200,000 years, studying ecosystem dynamics and the biogeochemical cycles in the terrestrial Arctic using multiproxy analyses of permafrost and lacustrine records.