Publisher Summary This chapter describes the methods commonly adopted to calculate doses from the different pathways. Several models have been developed for the particular aspects of the problem of calculating doses from material in inhabited areas, although none of the current available models address the pathways.The chapter deals with models used to calculate doses when radioactive material has contaminated a relatively large area, as might occur following an accident at a nuclear site or an event such as a fire or explosion involving radioactive material, including incidents caused by malevolent actions. The methods described are also appropriate for modelling other situations leading to a more localized contamination of part of the inhabited area. Models are needed for application to both routine and accidental releases. The simpler models are generally used to calculate doses from routine releases to the atmosphere. The more detailed models have been developed for application to accidental releases, primarily to provide an input into emergency planning, evaluation of countermeasure strategies, and to provide a tool for training.