The International Polar Year (IPY) 2007-2008 co-sponsored by ICSU and WMO became the largest coordinated research program in the Earth's polar regions. It involved a large range of disciplines, from geophysics to ecology, also embracing human health, social sciences, and the humanities. All IPY projects included partners from several nations and/or from indigenous communities and polar residents' organizations. An estimated 50,000 researchers, local observers, educators, students, and support personnel from more than 60 nations were involved in the 228 international projects (170 in science, 1 in data management, and 57 in education and outreach) and related national efforts. IPY generated intensive research and observations in the Arctic and Antarctica over a two-year period, March 1, 2007-March 31, 2009, with many activities continuing beyond that date. IPY 2007-2008 generated much anticipated momentum with substantial funding for research and monitoring activities, new observational and analysis technologies, integrated system-level approaches, and a broadened circle of stakeholders. It introduced new research and organizational paradigms that will have a lasting legacy of their own. It showed the power of integrative vision, and consolidated new trans-disciplinary approaches.