any of a class of organic compounds of the aromatic heterocyclic series characterized by a six-membered ring structure composed of five carbon atoms and one nitrogen atom. The simplest member of the pyridine family is pyridine itself, a compound with molecular formula C₅H₅N.

Pyridine is used as a solvent and is added to ethyl alcohol to make it unfit for drinking. It is converted to such products as sulfapyridine, a drug active against bacterial and viral infections; pyribenzamine and pyrilamine, used as antihistaminic drugs; piperidine, used in rubber processing and as a chemical raw material; and water repellents, bactericides, and herbicides. Compounds not made from pyridine but containing its ring structure include niacin and pyridoxal, both B vitamins; isoniazid, an antitubercular drug; and nicotine and several other nitrogenous plant products.

Pyridine occurs in coal tar, its principal source before development of a synthesis based on acetaldehyde and ammonia. The pure substance is a colourless, flammable, weakly alkaline, water-soluble liquid with an unpleasant odour; it boils at 115.5° C (234° F).