Description: Arctic sea ice is declining rapidly, simplifying access to oil and gas resources, enabling trans-Arctic shipping, and shifting the distribution of harvestable resources. This has brought the Arctic Ocean to the top of national and international political agendas. Alarmingly, sea-ice reductions are taking place more rapidly than predicted in any global climate model. This persistent mismatch between observed and predicted patterns makes planning and mitigation activities in the Arctic region even more complicated. Therefore, scientific knowledge of the present status of the Arctic Ocean and the process-based understanding of the mechanics of change are urgently needed to make useful predictions of future conditions throughout the Arctic region. The Arctic in Rapid Transition (ART) Initiative is an integrative, international, interdisciplinary, pan-Arctic network to study the spatial and temporal changes in sea ice cover and ocean circulation over all timescales to better understand and forecast the impact of these changes on the ecosystems and biogeochemistry of the Arctic Ocean. The ART Initiative was initiated in October 2008 and is still currently run by early-career scientists. After an ART Initiation Workshop in November 2009 a science plan was developed, since then endorsed by the Arctic Ocean Sciences Board: the Marine Working Group of the International Arctic Science Committee. To turn the approved ART science plan into reality an implementation plan was initiated during the ART Implementation Workshop in October 2010. The ART Initiative will take a phased approach. The first phase (~3–5 years) will focus on developing a formal scientific network to bring together scientists working in different geographic and disciplinary areas who share a common interest in improving our understanding of the implications of disappearing sea ice in the Arctic. This network will foster communication, scientific exchange and integrate results to tackle the questions outlined in the ART science plan. Phase II (~3–5 years) will implement dedicated, coordinated, dispersed, international, and interdisciplinary field campaigns. The final Phase III will be a synthesis stage including the conception of robust scenarios regarding the future state of Arctic marine ecosystems. Modeling will be an integral part throughout all three phases, as well as programs of mentoring and science planning educational programs to keep the identity of a program driven by early-career scientists. Ultimately, the integrative approach of ART will provide a means to better understand and predict changes in sea ice and ocean circulation and their consequences for biological productivity in the Arctic Ocean. The legacy of ART will be a robust set of predictive tools that will contribute to a reinforcement of Arctic marine sciences into global assessments of impact of climate change and increased human activity in the Earth System.