The EU FP7 Project EPOCA (European Project on OCean Acidification) was launched in May 2008 with the overall goal to advance our understanding of the biological, ecological, biogeochemical, and societal implications of ocean acidification. The EPOCA consortium brings together more than 100 researchers from 27 institutes and 9 European countries. The budget of this four year long project is 15.9 M ... €, including 6.5 M € from the European Commission. The research efforts of EPOCA will be implemented through 16 work packages separated into four themes. Theme 1 will focus on past and present spatiotemporal changes in ocean chemistry and biogeography of key marine organisms. Theme 2 will quantify impacts of ocean acidification on marine organisms and ecosystems and assess the potential for acclimation and adaptation. Theme 3 will improve biogeochemical, sediment, and coupled ocean-climate models to better account for how ocean acidification will affect ocean biogeochemistry and ecosystems. Finally, Theme 4 will synthesize results obtained in Themes 1, 2 and 3 for business leaders, policy-makers and the general public. It will evaluate uncertainties, risks and thresholds ("tipping points") related to ocean acidification at molecular, cellular and organismal levels and from local to global scales. It will also assess the decrease in CO2 emissions required to avoid these thresholds and describe the change to the marine environment and Earth system, should these emissions be exceeded.