[en] Highlights: • The X-ray absorption spectra of actinides are discussed with an emphasis atomic multiplet theory, charge transfer theory and crystal field theory. • Resonant inelastic X-ray emission spectra (RIXS) reveal many new features in the X-ray absorption spectra of actinides. • The new range of RIXS beamlines will become an important tool in the determination of the electronic structure of actinides. - Abstract: The X-ray absorption spectra of actinides are discussed with an emphasis on the fundamental effects that influence their spectral shape, including atomic multiplet theory, charge transfer theory and crystal field theory. Many actinide spectra consist of a single peak and it is shown that the use of resonant inelastic X-ray emission spectra (RIXS) has the potential to reveal many new features in the X-ray absorption spectra of actinides. The new range of RIXS beamlines will allow the determination of new structures in the X-ray absorption spectra that have been hitherto invisible. This has the potential to become an important tool in the determination of the electronic structure of actinides