Oxidative stress and reactive oxygen species play a major role in both normal and pathophysiologic cellular processes. Although many cellular constituents can be damaged by oxidant exposure, cysteine thiol groups are among the most readily oxidized moieties found within cells. To avoid potentially irreversible cysteine thiol oxidation, cells have developed multiple antioxidant defenses to preserve these moieties. Among these defenses, protein S-glutathiolation has emerged as an important mechanism, both in the maintenance of thiol stability during oxidant exposure and as a rapid and efficient mechanism regulating protein activity and cellular metabolic pathways. Here we review the known molecular targets of S-glutathiolation, with emphasis on the varying molecular effects of S-glutathiolation on different proteins.