The influence of the following parameters is discussed: oxidation state (Eh), hydrolysis (pH), solubility, complex formation, colloid formation, sorption and filtration effects. The oxidation states of the actinides in neutral aqueous media are plotted as a function of the redox potential. Hydrolysis, stability of 11 carbonato complexes, of humic acid complexes and solubilities of the hydroxides in the various oxidation states are considered. Mobility is investigated as a function of pH by paper chromatography. Partition of the actinides in groundwaters on the molecular fraction, the fine particle (colloid) fraction and the coarse particle fraction is determined as a function of pH by filtration and ultrafiltration. Sorption ratios are measured as function of pH, salt concentration and of EDTA concentration. When the groundwaters are passed through the sediments, mainly the coarse particle fractions are retained by size filtration. The pronounced influence of the redox potential on sorption is demonstrated for Np.