Over the years, radioactive particles have been released to the environment from nuclear weapons testing and nuclear fuel cycle operations. However, measurements of environmental radioactivity and any associated assessments are often based on the average bulk mass or surface concentration, assuming that radionuclides are homogeneously distributed as simple ionic species. It has generally not been recognised that radioactive particles present in the environment often contain a significant fraction of the bulk sample activity, leading to sample heterogeneity problems and false and/or erratic measurement data. Moreover, the inherent differences in the transport and bioavailability of particle bound radionuclides compared with those existing as molecules or ions have largely been ignored in dose assessments. There are currently no documents or international guides covering this aspect of environmental impact assessments. To fill this gap, between 2001 and 2008 the IAEA performed a Coordinated Research Programme (CRP- G4.10.0 3) on the ‘Radiochemical, Chemical and Physical Characterisation of Radioactive Particles in the Environment’ with the objective of development, adoption and application of standardised analytical techniques for the comprehensive study of radioactive particles. This IAEA-TECDOC presents the findings and achievements of the above CRP in the area of measurement and characterisation of radioactive particles in the environment.