The use of rigid receptors displaying preorganized cavities for the selective complexation of spherical ions has shown some limitations for trivalent lanthanide metal ions, LnIII, because of the minor variation of their ionic radii. The recent development of semi-rigid ligands derived from macrocyclic platforms grafted with complexing pendant arms or from tripodal podands leads to an unprecedented fine tuning of the structural, thermodynamic and electronic properties of the lanthanide complexes, thus opening new perspectives for the design of functional molecular or supramolecular devices. The application of the Induced fit concept for the design of covalent and non-covalent nine-coordinate monometallic and polymetallic podates is emphasized together with applications as light-converters, thermal and electrochemical switches and template agents. The step-by-step evolution from rigidity to flexibility in lanthanide coordination chemistry is presented and the basic recognition processes responsible for the tuning of the metallic site are discussed.