This document discusses affinity chromatography, a technique used to separate biomolecules. It was developed in 1968 using specific biological interactions between a molecule and immobilized ligand. The process involves binding the target molecule to the ligand, separating unbound molecules, and then eluting the target molecule. Affinity chromatography can purify targets from complex mixtures in a single step. It has been used to purify enzymes, nucleotides, antibodies, and more. The technique relies on reversible interactions between a target and ligand attached to a solid matrix. Proper selection of the matrix, ligand, and elution method are important for effective separation.