The IARC previously led an EU funded project “Agenda for Research on Chernobyl Health (ARCH)”, the objective of which was to recommend a strategic health research agenda following the Chernobyl accident. The ARCH demonstrated that Chernobyl provides a unique opportunity to answer questions about radiation risks. The multidisciplinary group of experts strongly supported the need for well-designed and coordinated long-term studies.The new initiative emphasises the need to build partnerships with the three countries mainly affected, plus Japan, the USA and European countries in order to take the research agenda forward. The purpose is therefore to bring together both key scientific players and funding partners to decide on the research priorities and to seek sustainable funding for those priority areas. Work under this proposal will be divided into five closely integrated work packages (WPs):WP 1: Coordination and overall managementWP 2: International collaboration and agreement on research programme• 2.1: Setting up an International network of research institutes committed to long-term research on Chernobyl• 2.2: Development of Chernobyl Research Programme and timetableWP 3: Assessment of Chernobyl research infrastructures• 3.1: Evaluation of the cohorts of exposed populations suitable to form Chernobyl Life-span cohorts• 3.2: Inventory of dosimetric approaches and existing databases• 3.3: Inventory of stored biological samplesWP 4: International collaboration on proposing funding mechanismWP 5: Agreement on coordinating structure and setting-up research frameworkThe CO-CHER project has a potential to develop a sustainable plan for research into the health effects of the Chernobyl accident with optimal use of available resources. It is completely in line with the MELODI initiative for integrated, long term effort in low dose risk research. The coordination action will also open new collaborations outside existing European networks.