The actinide elements pose a very interesting para­dox. Uranium and especially plutonium are materials that are very difficult to handle because of their radioactive nature, but they are among the most
extensively studied elements in the periodic table. This is of course due to the importance of these two elements in nuclear technology. The properties of the other actinides are relatively poorly known and are generally obtained from estimations. How­ever, due to the changes in the electronic properties of the 5f electrons, varying from delocalized to loca­lized, going from Th to Am, the systematics in the properties of the actinides are difficult to predict, and analogies with the 4f lanthanides are not (always) obvious. Theoretical predictions based on atomistic calculations could help to solve this, but the predic­tive potential of such calculations is still being explored. Clearly, more experimental studies are needed, particularly on the minor actinides.