The Arctic is undergoing the most rapid changes in the climate system globally, as shown by the thinning and reduction of sea ice, the melting of ice sheets and glaciers, thawing permafrost, and the potential for more extreme weather events. Given the complexity of Arctic ecosystems, reducing uncertainties in the long-term response of Arctic ecosystems to climate change requires an interdisciplinary study of the relationships among physical, chemical, biological, and human processes with an emphasis on the interactions among system components. This special issue collects contributions from a wide range of fields supported by the Horizon 2020 project INTAROS (Integrated Arctic Observation System), including ocean and sea ice, atmosphere, the terrestrial sphere (e.g. patterns and controls of greenhouse gas emissions and their response to climate change particularly during the cold season), and the cryosphere. The ocean studies will be complemented by a wide range of other studies across the cryosphere, the atmosphere, and the terrestrial Arctic systems. The goal is to produce an integration of multi-disciplinary observations in the Arctic and report on innovative analysis and methods which can stimulate new products and improved services and to demonstrate the benefit of a continuous long-term effort in these observations to assess the temporal changes across the Arctic.