[en] Speciation refers to the use of different fractionation techniques by which information on radionuclide species can be obtained. Techniques fractionating species according to size and charge properties allows information on size classes and reactivity classes to be obtained. Fractionation of radionuclides should take place in situ, at site or shortly after sampling. There are some few in situ size fractionation techniques for radionuclides in waters. In sea water large capacity (tangential flow systems) is needed, while hollow fibre systems can often be applied for rivers and lakes. By interphasing chromatographic systems (ion exchange columns) with hollow fibres, in situ sampling, size and charge fractionation can be performed simultaneously. For small volume soil waters in situ suction techniques may suffer from methodological effects. Structural information on radioactive particles or colloids can be attained by using different electron microscopy techniques. Separation of radionuclide species in solid samples is still an analytical challenge. Grain size analysis and determination of radionuclides associated with the sand, silt, clay and colloidal fractions should be combined with sensitive surface analytical techniques. Reactivity studies using extraction reagents can be useful for distinguishing between reversible and irreversible (or slow reversible) kinetics processes. Repeated extractions with inert electrolytes (or by lowering pH gradually) should reflect if reversible processes (e.g. physical, electrochemical sorption) take place. In contrast, information on irreversible processes (e.g chemisorption) is obtained if strong red/ox agents are needed for dissolution of species (binding rupture). The paper will focus on available size or charge fractionation techniques which should be useful within radioecology