This book constitutes the refereed proceedings of the 12th IFIP WG 6.1 International Conference on Distributed Applications and Interoperable Systems, DAIS 2012, held in Stockholm, Sweden, in June 2012 as one of the DisCoTec 2012 events. The 12 revised full papers and 9 short papers presented were carefully reviewed and selected from 58 submissions. The papers are organized in topical sections on peer-to-peer and large scale systems; security and reliability in web, cloud, p2p, and mobile systems; wireless, mobile, and pervasive systems; multidisciplinary approaches and case studies, ranging from Grid and parallel computing to multimedia and socio-technical systems; and service-oriented computing and e-commerce.