This publication presents the work and activities undertaken by Working Group 7 (WG7) of the IAEA’s EMRAS II Programme and considers the conclusions drawn during EMRAS Phase I, 2003–2007. The working group members tested and compared environmental transfer models to be applied after short term releases of tritium from nuclear power plants in order to estimate exposures through inhalation of contaminated air and the ingestion of contaminated food. The main goal was to develop a harmonized, robust model for practical applications. The publication delineates all relevant processes as well as the analyses and evaluated models for the environmental transfer of tritium, and identifies sources of and quantifies model uncertainties. The present status and needs are summarized and further fields of activity are identified to improve the reliability and the application of models to assess tritium behaviour and the resulting radiological impacts to people and the environment.