Salicylic acid (SA) is a natural phenolic compound in plants that plays a crucial regulatory role in plant immune responses. Plants primarily synthesize SA through two pathways: the isochorismate synthase (ICS) pathway and the phenylalanine ammonia-lyase (PAL) pathway. The synthesized SA is perceived by receptors such as nonexpressor of pathogenesis-related genes 1 (NPR1), which subsequently activate immune responses. In Brassicaceae species like Arabidopsis thaliana, SA is mainly synthesized via the ICS pathway, whereas monocots and non-Brassicaceae dicots predominantly rely on the PAL pathway. For a long time, understanding of SA biosynthesis via the PAL pathway has been incomplete, hindering research on SA-mediated immunity in crops and significantly limiting progress in crop disease-resistant breeding. Recently, three research groups from China independently elucidated the PAL-mediated SA biosynthesis pathway in crops. Building on these breakthroughs, this review summarizes recent advances in the study of SA-mediated plant immune responses. We primarily focus on the biosynthetic pathways of SA within plants, the mechanisms by which SA is perceived and activates immune responses, and discuss current challenges and future directions in SA-mediated immunity research. We hope this review provides new insights and perspectives for both theoretical studies and practical applications in crop disease-resistant breeding.