Lignin is a major component of plant cell walls, contributing to plant growth, tissue/organ development, lodging resistance, and stress responses. This review systematically introduces the biosynthesis of lignin, its regulation by genetic modification, and its biological functions in plants. Lignin biosynthesis involves three processes: monomer biosynthesis, transport, and polymerization. Genetic modification of lignin biosynthesis genes can alter lignin content and composition, affecting plant growth and development. Lignin plays crucial roles in plant growth and development, lodging resistance, and stress tolerance. It enhances cell wall rigidity, hydrophobicity, and mineral transport, and acts as a barrier against pests and pathogens. Lignin accumulation is important for seed propagation and protects seeds from external factors. Insect and disease resistance are enhanced by lignin accumulation, which forms a barrier or is regulated by hormone signaling pathways. Lignin also contributes to heavy metal tolerance by binding to metal ions and reducing their entry into the cytoplasm. Under drought and salt stress, lignin reduces water penetration and transpiration, maintaining cell osmotic balance. Temperature stress adaptation involves lignin deposition in the terminal latewood tracheid and heat and low temperature conditioning. Different types of lignin, such as softwood, hardwood, and grass lignin, have distinct monomer compositions, affecting their degradability and applications. The review highlights the importance of lignin in plant biology and its potential for improving crop yields and bioenergy efficiency through genetic engineering.Lignin is a major component of plant cell walls, contributing to plant growth, tissue/organ development, lodging resistance, and stress responses. This review systematically introduces the biosynthesis of lignin, its regulation by genetic modification, and its biological functions in plants. Lignin biosynthesis involves three processes: monomer biosynthesis, transport, and polymerization. Genetic modification of lignin biosynthesis genes can alter lignin content and composition, affecting plant growth and development. Lignin plays crucial roles in plant growth and development, lodging resistance, and stress tolerance. It enhances cell wall rigidity, hydrophobicity, and mineral transport, and acts as a barrier against pests and pathogens. Lignin accumulation is important for seed propagation and protects seeds from external factors. Insect and disease resistance are enhanced by lignin accumulation, which forms a barrier or is regulated by hormone signaling pathways. Lignin also contributes to heavy metal tolerance by binding to metal ions and reducing their entry into the cytoplasm. Under drought and salt stress, lignin reduces water penetration and transpiration, maintaining cell osmotic balance. Temperature stress adaptation involves lignin deposition in the terminal latewood tracheid and heat and low temperature conditioning. Different types of lignin, such as softwood, hardwood, and grass lignin, have distinct monomer compositions, affecting their degradability and applications. The review highlights the importance of lignin in plant biology and its potential for improving crop yields and bioenergy efficiency through genetic engineering.