Lignin is a major component of plant cell walls, a complex phenolic polymer with high molecular weight and diverse composition. It plays critical roles in plant growth, development, and resistance to biotic and abiotic stresses. Lignin biosynthesis involves three main processes: monomer synthesis, transport, and polymerization. Genetic modification can alter lignin content and structure, influencing plant traits such as lodging resistance, disease resistance, and stress tolerance. Key enzymes in lignin biosynthesis include peroxidases (POD) and laccases (LAC), which are crucial for polymerization. Transcription factors like MYB and NAC regulate lignin biosynthesis, affecting cell wall formation and plant development. Lignin also contributes to plant mechanical strength, water transport, and protection against pests and pathogens. In terms of stress adaptation, lignin biosynthesis is involved in plant responses to drought, salt, heavy metals, and temperature changes. Lignin can act as a barrier or through hormone signaling pathways to enhance plant resistance. Additionally, lignin has applications in energy and pharmaceutical industries. However, reducing lignin content can negatively impact plant growth and stress resistance. Future research should focus on balancing lignin levels to improve plant performance and bioenergy efficiency. This review summarizes the biosynthesis, regulation, and biological functions of lignin in plants, highlighting its importance in plant biology and applications.Lignin is a major component of plant cell walls, a complex phenolic polymer with high molecular weight and diverse composition. It plays critical roles in plant growth, development, and resistance to biotic and abiotic stresses. Lignin biosynthesis involves three main processes: monomer synthesis, transport, and polymerization. Genetic modification can alter lignin content and structure, influencing plant traits such as lodging resistance, disease resistance, and stress tolerance. Key enzymes in lignin biosynthesis include peroxidases (POD) and laccases (LAC), which are crucial for polymerization. Transcription factors like MYB and NAC regulate lignin biosynthesis, affecting cell wall formation and plant development. Lignin also contributes to plant mechanical strength, water transport, and protection against pests and pathogens. In terms of stress adaptation, lignin biosynthesis is involved in plant responses to drought, salt, heavy metals, and temperature changes. Lignin can act as a barrier or through hormone signaling pathways to enhance plant resistance. Additionally, lignin has applications in energy and pharmaceutical industries. However, reducing lignin content can negatively impact plant growth and stress resistance. Future research should focus on balancing lignin levels to improve plant performance and bioenergy efficiency. This review summarizes the biosynthesis, regulation, and biological functions of lignin in plants, highlighting its importance in plant biology and applications.