IUPAC gives several different definitions of oxidation: loss of electrons, increase in oxidation state, loss of hydrogen, or gain of oxygen. Most introductory or general chemistry textbooks use all of these definitions at one time or another, which can lead to some confusion in the minds of first-year chemistry students. Some paradoxical "exceptions" to these definitions of oxidation include (i) real electrons are not always lost in oxidations; (ii) some hydrogen and oxygen transfer reactions are not redox reactions; and (iii) in oxidations that involve gain of oxygen, the oxygen atom is not always the oxidant. The "increase in oxidation state" definition of oxidation is the only one that has no exceptions; furthermore, only by identifying oxidation state changes can students balance redox equations and count the number of electrons transferred. Accordingly, oxidation state changes should be the primary definition that we use in introductory or general chemistry to teach the concept of redox reactions. (Contains 1 scheme and 3 notes.)