CalMarO aims at the comprehensive training of twelve young researchers in the field of calcification by marine organisms based on a Network of thirteen research institutions and four SMEs. The Network participants are acknowledged experts with complementary research or commercial approaches in this field. Calcification is a fundamental physiological process of marine organisms that is largely determined by the characteristics of seawater. Calcifying marine organisms differ in their adaptability to variations in environmental conditions, in particular temperature and seawater pH. If global CO2 emissions continue to rise at current trends seawater pH may decrease to levels that are probably lower than have been experienced for tens of millions of years and, critically, at a rate of change 100 times greater than at any time over this period, with dramatic effects on productivity and marine ecosystems. CalMarO comprises investigation of calcification processes and the sensitivities to changes in environmental conditions at all scales ranging from cellular, organism, population to ecosystem, and regional to global levels. Covering this important topic in a training Network will offer young researchers an integrated perspective on an emerging problem and position their own work within the framework of a concerted effort to better understand the risks and consequences associated with ocean change. Three pillars support the training programme: personalised programmes, Network activities and dissemination. The principle of co-supervision by at least two senior scientists and SME placement on the basis of an individual mentoring plan represents the core piece of the training programme, with links to joint activities across the Network. These include annual meetings and theme oriented workshops. CalMarO participants will disseminate the Network achievements in a special session at a major conference and a major joint publication.