Plasma etching of organic polymers typically involves the use of feed gas mixtures of oxygen with a fluorocarbon. The reactive etchants are generally accepted to be atomic fluorine and atomic oxygen. The roles of these etchants are discussed with special attention being given to the part played by atomic fluorine. Mechanisms are inferred theoretically from a molecular orbital study, and experimentally from the surface composition of plasma treated samples. Hydrogen abstraction by fluorine leads to enhanced etching of saturated polymer structures while addition of fluorine is the dominant mechanism for unsaturated moieties. Etch rate behavior for polyimide, polyisoprene, and polyethylene as a function of gas composition is discussed in terms of the affinity that fluorine has for the surface of the saturated and unsaturated polymers.