This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above effects are taken into account, the pattern of ionization energies of the lanthanide elements is similar to that of the main group elements and increases across the period from left to right. (Contains 2 notes, 3 tables, and 8 figures.)