This publication has been produced as part of the IAEA's Modelling and Data for Radiological Impact Assessments (MODARIA) programme. It summarizes the activities of Working Group 7, which was one of ten working groups within MODARIA, and focused on the harmonization and intercomparison of models for the accidental release of tritium to the atmosphere. It addresses the modelling of tritium into the atmosphere and the subsequent terrestrial processes...