The vast sweep of phosphate chemistry in biological systems, from energy metabolism to the covalent connectivity in DNA and RNA, to the polar head groups of membrane phospholipids, and to the >250 000 predicted phosphorylation sites in the canonical human phosphoproteome, involves only four major types of phosphate compounds. Inorganic phosphate as the monoanionic and dianionic form of the inorganic mineral acid H₃PO₄ is the default state, presenting both a central electrophilic phosphorus (P^V oxidation state) and one or two peripheral oxyanion nucleophiles. It is a substrate for the energy-generating mitochondrial ATP synthase and for oligo-and polysaccharide phosphorylases. The kinetically stable but thermodynamically activated phosphoric anhydrides, presumably in the form of naked inorganic pyrophosphate in early evolution, and in ATP (and GTP and UTP and CTP congeners) for the past eons, are the diffusible energy currencies in cells, spent for almost every cellular need. The third class are phosphate monoesters. They dominate carbohydrate metabolism from initial trapping of glucose as intracellular glucose-6-phosphate. Glucose-6-phosphate is then partitioned down three distinct metabolic pathways – glycolysis to provide energy, to ribose-5-phosphate to build nucleotide precursors of RNA and DNA, or to glucose-1-phosphate for glycoprotein and polysaccharide metabolism. The fourth and remaining phosphorus derivative of biological centrality is the phosphodiester group, linking two alcohols by way of the intermediate –PO₂– bridge.