One of the most pressing and fascinating challenges scientists face today, is understanding the complexity of our globally interconnected society. The Big Data arising from human activities promise to let us investigate the ground truth of individual and collective behaviour at an unprecedented detail and scale. There is an urgent need to harness these opportunities for scientific advancement and for the social good. The main obstacle to this accomplishment, besides the scarcity of data scientists, is the lack of a large- scale open infrastructure, where big data and social mining research can be carried out. To this end, SoBigData Research Infrastructure project (CNR, Scuola Normale Superiore, Pisa University and IMT Lucca) proposes to create the Social Mining & Big Data Ecosystem: a Research Infrastructure providing an integrated ecosystem for ethic-sensitive scientific discoveries and advanced applications of social data mining on the various dimensions of social life, as recorded by “big data”. SoBigData will open up new research avenues in multiple research fields, including mathematics, ICT, and human, social and economic sciences, by enabling easy comparison, re-use and integration of state-of-the-art big social data, methods, and services, into new research. It will create a pan-European, inter-disciplinary community of social data scientists, fostered by extensive training, networking, and innovation activities.