Radiological environmental impact assessment models are important tools to ensure protection of the public and the environment. The IAEA has an ongoing programme to improve capabilities in this area by model testing and comparison, reaching consensus on modelling philosophies, approaches and parameter values. This publication describes and summarizes the findings of Working Group 9 carried out during the IAEA EMRAS II (Environmental Modelling for Radiation Safety) programme. The results presented draw on international model validation exercises conducted to test and improve the predictive ability of models used for the assessment of radioactive contamination in urban settings, including dispersion and deposition events, short and long term contaminant redistribution following deposition events, and the effectiveness of potential countermeasures (protective actions, including remedial actions) for reducing human exposures.