CHAIN is a large scale integrating project aimed to effectively and durably combat new and existing anti-HIV drug resistance in clinical settings, with a special emphasis on Eastern Europe and in heavily affected resource-poor regions in Africa. This will be achieved through our pan-European network of surveillance and basic research activities, the involvement of all main actors in the field of HIV and anti-HIV drug resistance, monitoring how resistances develop and evolve, improved understanding of mechanisms of resistance development, performing molecular epidemiology studies, providing improved and new strategies to evaluate and limit the emergence and transmission of HIV drug resistance, setting up training and dissemination activities and supporting evidence-based public health policy and action. CHAIN brings together Europe’s leading internationally recognised scientific expertise in basic science, molecular epidemiology, bioinformatics and surveillance of HIV and HIV resistance including the WHO, strong links to Eastern Europe through the existing FP6 funded cohort network Europe HIVresistance and strategic links to relevant pan-European cohort networks and national cohort networks (PENTA/ECS, CASCADE, EuroSIDA, COHERE, ICoNa, UK-CHIC, SHCS). Our balanced programme of work is informed by optimising the synergistic skills represented by the applicants, and also through harmonising with existing initiatives, that ensures lack of duplication, but rather maximises the impact of European activities. Thus, our African and Eastern European work will be linked to WHO policy, our European surveillance studies will be guided by ECDC (through our advisory board), and our clinical research will generate questions best addressed through the NEAT clinical trial network. Finally, our partnership with the key biotechnology companies in HIV resistance will ensure maximal impact of our basis research activities.