Salicylic acid (SA) and methyl jasmonate (MJ) signaling is associated with phospholipids and the enzymes that metabolize them. However, despite the many studies conducted, the role of SA or MJ signalling via phospholipids in plant responses is not yet fully understood. The signaling pathways of SA and MJ have been evaluated in plant cell suspensions, and it was observed that these compounds regulate enzymatic activities to generate a rapid cellular response. This book discusses the immune responses induced by salicylic acid and jasmonic acids against plant parasites; the induction by SA of in vitro thermotolerance during thermotherapy; aalicylic acid, methyl jasmonate and phospholipid signaling in suspension cells; the self-association of salicylic acid derivatives in aqueous solutions studied by methods of absorption and fluorescence; and the role of exogenous salicylic acid applications for salt tolerance in tomato plants.