Phosphorus polymers and oligomers are surveyed with emphasis on methods of synthesis and utility. Red phosphorus is a useful flame‐retardant insoluble polymer. Polyphosphoric acid has catalytic utility, and its salts find use in chelation and flame retardancy. Phosphorus‐nitrogen polymers and oligomers may be involved in the synergistic flame‐retardant action of combinations of phosphorus and nitrogen compounds, such as on cellulose. Lower‐oxidation‐state organic phosphorus polymers and oligomers such as phosphines and phosphites have stabilizer and catalyst utility. Higher‐oxidation‐state phosphorus polymers and oligomers such as phosphates and phosphonates, made mainly by condensation reactions, have flame‐retardant utility in plastics as additives and reactive modifiers, and also in as textile additives and finishes.