The Arctic Summer Cloud Ocean Study (ASCOS) was a scientific expedition to the high Arctic in summer 2008, during the International Polar Year (IPY) and was deployed on the Swedish icebreaker Oden. The main targets was to study the formation and life cycle of low-altitude Arctic clouds in the central Arctic. The expedition was by necessity highly interdisciplinary, and covered observations of the physics and chemistry of the atmosphere and the upper ocean, meteorology, cloud microphysics and aerosols, and upper-ocean biogeochemistry. ASCOS was likely the largest single Arctic Ocean atmospheric effort during the IPY an was endorsed under the AICI-IPY umbrella under SOLAS.