From an experimental point of view, there have been impressive improvements on the synthesis procedure and more importantly on the chemical stabilization of the synthesized complexes. Density functional theory (DFT) in particular is an important tool for the prediction of electronic structures, plausible mechanisms, and spectroscopic data involving complexes of d‐transition, lanthanide, and actinide metals. The ground state electronic structure is determined by how the biradical correlates the two electrons, either forming a triplet state (MS = 1) or an open‐shell singlet state. Theoretical approaches have been extensively used to predict the nature of the ground state of several Yb(II) complexes, using the multireference CASSCF method. DFT methods can be used to describe and explain the reactivity of actinide complexes, even when single electron transfer (SET) is involved. In particular, the geometry and the electronic structure of cyclopentadienyl complex which are very important in organoactinide chemistry are correctly reproduced.