The idea of effective core potentials (ECPs) is based on the chemically intuitive restriction of the explicit calculations to the chemical important valence electrons, while the essentially inert atomic cores, i.e., the nucleus and the electrons in the inner shells, are replaced by a suitable parametrized (relatively simple) one‐electron operator acting on the remaining valence electrons, i.e., the effective core ‘potential’. This chapter emphasizes only those modern variants of the pseudopotential (PP) approach, which experience a widespread use for f elements. It summarizes the most important concepts and equations of the PP method. The chapter describes in detail the two different kinds of PP adjustment, i.e., the energy‐ and shape‐consistent technique. It briefly comments on the valence basis sets for PP calculations. The chapter shows some characteristic applications, and finally, it gives a short conclusion and outlook demonstrating the possibilities and limitations of the PP approach.