Hydroxyapatite [Ca10(PO4)6(OH)2] is an inorganic pure-phase chromatography resin, which consists of spheres calcined at high temperatures. Its crystal structure is the same as that of hydroxyapatite in bone, with stable spherical structure and uniform particle sizes. Hydroxyapatite can interact with biomolecules in multiple modes to realize two separation mechanisms simultaneously: cation exchange and calcium metal affinity. The cation exchange mainly depends on the negatively charged phosphate groups on hydroxyapatite. Also, carboxyl clusters and phosphorus clusters on biomolecules can form stronger bonds with calcium on hydroxyapatite through metal affinity. Due to these unique separation mechanisms, hydroxyapatite has become an indispensable chromatography resin in today's extremely demanding downstream processes and plays an important role in the fields of biopharmaceuticals such as antibodies, vaccines (bacterial polysaccharides, pneumonia polysaccharides, and viruses), nucleic acids, enzymes, and recombinant proteins.