Tetracyclines are a group of broad-spectrum antibiotics whose general usefulness has been reduced with the onset of antibiotic resistance. Despite this, they remain the treatment of choice for some specific indications.

They are so named for their four (“tetra-”) hydrocarbon rings (“-cycl-”) derivation (“-ine”). To be specific, they are defined as "a subclass of polyketides having an octahydrotetracene-2-carboxamide skeleton". They are collectively known as "derivatives of polycyclic naphthacene carboxamide".