Salicylic acid (SA) is a plant hormone more commonly known by its role in human medicine than in the field of plant physiology. However, in the last two decades, SA has been described as an important signalling molecule in plants regulating growth, development and response to a wide number of biotic and abiotic stresses. Indeed, actually, it is well known that SA is a key signalling molecule involved in systemic acquired resistance (SAR), and recent works reported a role for SA in the response to salt or drought stresses. The precise mode of the stress hormone SA action is unclear, although it has been shown to interact in a complex manner with the antioxidative metabolism, modulating cellular redox homeostasis and leading to changes in transcription factor activities and defence gene activation. In this sense, SA activates defence signalling pathway(s) through non-expressor of PR-protein 1 (NPR1), which is one of the few known redox-regulated proteins in plants. Different synthetic chemicals are able to mimic the ability of SA to activate resistance to various stresses, both biotic and abiotic, in plants with agronomic interest. Among these chemicals, 2,6-dichloroisonicotinic acid (INA) and benzothiadiazole (BTH) are the most widely studied compounds due to its ability to induce SAR. In this chapter we present the role of SA and/or some of its structural analogues in the response to some biotic and abiotic challenges in relation to their effect in the antioxidative metabolism in plants.