Analyte molecules that displace ligands from a metal center immobilized on a chelating stationary phase, or that coordinate to a metal ion in the eluent, constitute ligand-exchange chromatography (LEC). The metal—commonly Cu(II), Zn(II), or a surface metal on zirconia—presents vacant coordination sites; solutes with donor atoms (amino acids, sugars, enantiomeric drugs) form transient complexes whose stability constants differ, and those differences become chromatographic selectivity ^[1]. Chiral LEC uses a chiral ligand or a chiral mobile-phase additive around the metal to resolve enantiomers ^[2]. Conceptual boundaries exclude immobilized-metal affinity chromatography that captures histidine-tagged proteins on Ni(II) or Co(II) without a ligand-exchange elution of small donor solutes as the defining mode, and they exclude ordinary ion-exchange chromatography. Essential features are a defined metal–ligand coordination sphere, reversible exchange of that sphere with the analyte, and a mobile phase that supplies competing ligands or protons to release the solute ^[3]. Lewis acid–base binding of carboxylates on zirconia is a related ligand-exchange process on an oxide surface ^[4].