[en] Theoretical and experimental work on the nature of the 5f electrons in the actinide series is reviewed briefly. It is suggested that intra-atomic coulomb repulsion between 5f electrons is of great importance in the actinides and quantitative support is given to the itinerant picture of the 5f states already found in band structure calculations. The effective intra-atomic interaction is calculated by the same method as applied to cerium in earlier work. The question of valencies in the actinides is discussed; the appearance of superconductivity is correlated with the f-bandwidth. 19 references