The response of plants to ozone exposure includes a number of physiological and biochemical changes that are the direct result of selective increases or decreases in gene expression and the resulting changes in the accumulation of the corresponding protein products. Major classes of ozone-induced proteins include antioxidant enzymes and a number of stress-related proteins associated with other biotic and abiotic stresses. In particular, there is a significant overlap in the pattern of gene induction observed in ozone-treated plants and plants exhibiting pathogen defense responses. Current knowledge concerning the specific molecular events associated with the alterations of gene expression caused by ozone and the precise roles of ozone-induced proteins in conferring tolerance to ozone is rather limited. This review summarizes some of the recent results that have been obtained concerning the molecular basis of ozone-induced responses in plants, with an emphasis on studies of the model plant system, Arabidopsis thaliana. These studies demonstrate that ozone-induced responses are caused in part by the activation of a salicylic acid dependent signaling pathway that is also required for the expression of resistance to microbial pathogens.