The aim of this overview paper is to provide a brief synthesis of the five review papers contained in the monograph. Prevailing southwesterly winds, oceanic flow patterns, and oceanic summer heat storage make the temperatures of the Nordic Seas region 10-20°C above the mean temperature of locations at similar latitudes. The combination of the large heat import from the south plus the polar location implies that the region is prone to natural climate variations and is particularly vulnerable for external forcings. Indeed, proxy data for the Holocene epoch reveal large, high-frequency climate fluctuations, as well as long-term variations spanning the "Medieval Warm Period" and the "Little Ice Age". In phase with a strengthening of the westerly winds since the 1960s, several oceanic key variables show trends unprecedented in available instrumental records, some of which extend back 50-100 years. State-of-the-art climate models indicate that several of the changes may be linked to increased forcing of greenhouse gases and are therefore likely to be sustained or even amplified in the future. Furthermore, the marine cycling of carbon, and through that the major greenhouse gas carbon dioxide, is closely linked to the climate state of the region. The Nordic Seas region is, as one of few ocean locations, a sink for atmospheric carbon dioxide throughout the year. With the rapid developments in data acquisition, computational resources, and societal concerns for climate change and environmental issues, the review papers give an updated account of the present knowledge of the complex climate states of the Nordic Seas and how the Nordic Seas influence the climate outside the region.