The energy of the 4f-5d transitions of divalent and trivalent lanthanide impurities in compounds depends strongly on the type of lanthanide, its valence, and the type of compound. Despite this large variability there is much systematic in 4f-5d transition energy. Once it is known for one lanthanide that for all others when in the same compound can be predicted. The same applies for the energy of electron transfer from the valence band to the 4f-shell of lanthanides which also behaves in a systematic fashion with type of lanthanide and type of compound. This work reviews my studies during the past fifteen years that are based on an analysis of data on all divalent and all trivalent lanthanides in more than 1000 different inorganic compounds collected from the archival literature. The established redshift and charge transfer models that form the basis to construct binding energy schemes showing all lanthanide levels with respect to the host bands are reviewed and the latest developments are addressed.