This publication reports on the outcome of an IAEA coordinated research project in the area of measurement and characterization of radioactive particles in the environment. It summarizes the achievements and findings of the project participants and gives guidance for application of the techniques for evaluation of contaminated areas. Furthermore, it describes the main sources of radioactive particles in the environment and presents the results of worldwide case studies on characterization of radioactive particles from different sources based on the application of the techniques described in the publication. The information provided will be useful for radioecologists, radiation protection specialists and experts who are responsible for assessment of radiation impacts on humans and non-human species.