Lignin is a complex, three-dimensional biopolymer found in plant cell walls, playing a crucial role in agriculture and industry due to its applications in pulping, forage digestibility, biofuel, and carbon sequestration. Recent research highlights its diverse roles in plant defense against pathogens. This review discusses the biosynthesis of lignin and its functions in disease resistance. Lignin biosynthesis involves a complex pathway starting with the deamination of L-phenylalanine or tyrosine into cinnamic acid, followed by a series of reactions to produce monolignols, which polymerize into lignin. Key enzymes in this pathway include phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and ferulate 5-hydroxylase (F5H). Lignin's structure and composition vary among plant species, influencing its role in defense responses. Lignin acts as a physical barrier against pathogens, and its synthesis is induced by various stresses. Additionally, lignin-related compounds and genes contribute to plant immune responses, including the production of phytoalexins and the regulation of defense signaling pathways. The review also explores the molecular mechanisms underlying lignin's role in disease resistance, emphasizing the importance of lignin in plant development and defense. Understanding these mechanisms can aid in developing broad-spectrum resistant crops through molecular breeding strategies.Lignin is a complex, three-dimensional biopolymer found in plant cell walls, playing a crucial role in agriculture and industry due to its applications in pulping, forage digestibility, biofuel, and carbon sequestration. Recent research highlights its diverse roles in plant defense against pathogens. This review discusses the biosynthesis of lignin and its functions in disease resistance. Lignin biosynthesis involves a complex pathway starting with the deamination of L-phenylalanine or tyrosine into cinnamic acid, followed by a series of reactions to produce monolignols, which polymerize into lignin. Key enzymes in this pathway include phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and ferulate 5-hydroxylase (F5H). Lignin's structure and composition vary among plant species, influencing its role in defense responses. Lignin acts as a physical barrier against pathogens, and its synthesis is induced by various stresses. Additionally, lignin-related compounds and genes contribute to plant immune responses, including the production of phytoalexins and the regulation of defense signaling pathways. The review also explores the molecular mechanisms underlying lignin's role in disease resistance, emphasizing the importance of lignin in plant development and defense. Understanding these mechanisms can aid in developing broad-spectrum resistant crops through molecular breeding strategies.