DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies) aimed at reducing the uncertainties in our understanding, modeling and forecasting of climate changes in the Arctic. Over the last 2–3 decades the Arctic has warmed more than other regions of the world and the Arctic sea-ice cover has decreased significantly in the same period. DAMOCLES was especially concerned with a significantly reduced sea-ice cover and the impact this drastic sea-ice retreat might have on the environment and on human activities both regionally and globally. A first-order scientific and societal question is whether the Arctic perennial sea-ice will disappear in a few decades (or even faster as predicted by some state-of-the-art models). The changing Arctic climate has and will continue to have a wide range of impacts on human activities such as fisheries, shipping, as well as offshore oil and gas development at local, regional, national and international levels. DAMOCLES aimed at analyzing the adaptation to and vulnerability of human activities in the context of physical changes such as a sea-ice extent and concentration decrease, an ice free ocean and elevated air temperature. Through its regional, multidisciplinary approach, DAMOCLES intended to provide a broad perspective for decision-makers and stakeholders in considering future policies for adaptation. Adaptation and mitigation requires specific information, preferably early information. The coordinated analysis of observations and model simulations achieved during DAMOCLES, aims at facilitating the design of a future cost-effective and sustainable Arctic observing and forecasting system. The Arctic is a harsh environment and the sea-ice cover prohibits the use of many conventional instruments, data transfer methods and calibration schemes. DAMOCLES developed new technology to get observations of key variables in the atmosphere, sea-ice and in the ocean. DAMOCLES brought together experts on polar research and a broad range of environmental modelers through an integrated research effort. The effort complemented other major research programs on climate variability and predictability. At a time when the International Polar Year focused on the science of the polar regions and on the human dimension of climate change, DAMOCLES provided a contribution reflecting both the skills of European scientists and the importance of European interests for the Arctic. The EU DAMOCLES project lasted for 54 months from 1 December 2005 until 30 May 2010. It involved 51 partners including 8 small and medium enterprises spread over 10 European countries and coordinated with the United States, the Russian Federation, Canada and Japan. During the course of the project 152 peer-reviewed scientific papers were published, 302 deliverables were submitted to the EU Commission, 52 workshops and 8 summer schools were organized. 30 students passed their PhD examination. In addition to DAMOCLES, a Scientific Supported Action (SSA) “SEARCH for DAMOCLES” (S4D) gathering European and US scientists, a Third Targeted Countries (TTC) initiative bringing scientists from Russia and Belarus together with DAMOCLES partners and a MoU (Memorandum of Understanding) with China, were established. The DAMOCLES activity culminated during the International Polar Year (2007–2008) at a time of a phenomenal sea ice retreat in the summer of 2007 when the French schooner Tara accomplished a transpolar Arctic drift in about 500 days compared to a 3 year drift (approximately 1000 days) of Nansen’s Fram more than a century ago. The Tara transpolar drift that started on September 2006 in the Laptev Sea and ended on January 2008 in the Greenland Sea, stimulated a number of peerreviewed outstanding scientific papers. Twenty papers were selected for a book specially dedicated to the Tara DAMOCLES enterprise. The SSA S4D launched the first initiative for the so-called September Sea Ice Outlook consisting in