While some transition d-block elements are known and used since millenniums, the first f-block analogues were discovered after the French revolution. Their reluctance toward reduction forced the early chemists to develop separation techniques relevant to what will become coordination chemistry at the turn of the ninetieth century. In the absence of satisfying model for rationalizing the trends in the associated thermodynamic complexation processes, the coordination chemistry of trivalent rare earth remains exploratory and empirical for a long period. In a seminal review published in the first set of four volumes of the Handbook, Thompson elegantly highlighted the gap between the demanding requirements of separation processes and the limited understanding of simple lanthanide–ligand interactions (Thompson, 1979). During the past 35 years, the well-established main stream approach focused on the systematic characterization and isolation of rare earth complexes with myriads of novel ligands benefited from the parallel development of enthalpy/entropy correlations and of supramolecular chemistry. This contribution reports on the most important innovation brought by these novel ideas for the design, the stability, and the rationalization of rare earth complexes.