Lignin is a polymer formed from monolignols derived from the phenylpropanoid pathway in vascular plants. It is deposited in the cell walls of plants as part of the process of cell maturation. Lignin is considered an anti-quality component in forages because of its negative impact on the nutritional availability of plant fiber. Lignin interferes with the digestion of cell-wall polysaccharides by acting as a physical barrier to microbial enzymes. Lignification therefore has a direct and often important impact on the digestible energy (DE) value of the forage. There are a number of plant-related factors that affect lignification in individual plants and plant communities. Lignification is under genetic control and there are considerable differences in lignin concentration and composition among species and even genotypes within species. Genetic differences in lignification are first expressed at the cellular level and are affected by biochemical and physiological activities of the cell. As cells differentiate, differences in lignification occur depending on the tissues and organs being developed. Lignification tends to be most intense in structural tissues such as xylem and sclerenchyma. Plant organs containing high concentrations of these tissues, such as stems, are less digestible than those containing lower concentrations. The relative proportion of lignified tissues and organs typically increases as plants mature so there is often a negative relationship between digestibility and maturity. All of these plant processes respond to environmental factors that can affect the extent and impact of lignification. Temperature, soil moisture, light, and soil fertility can have either direct or indirect effects on lignification. The most useful management practices for minimizing the negative effects of lignification are manipulation of the plant community such that it contains more desirable species and harvest management to maintain plants in a vegetative stage of development. Key Words: Anti-quality, digestibility, forage quality, forage utilizationLignin is considered an anti-quality component in forages because of its negative impact on the nutritional availability of plant fiber. It differs from most other classes of antiquality components in forages in that it is a structural compound rather than a secondary metabolite. Its evolution in plants is primarily related to plant structure and function and not as a defense mechanism against other organisms. As a component of the cell wall, lignin plays an important role in morphogenesis. Cell walls form the structural framework of the plant architecture that provides mechanical support for plant organs (Varner and Lin 1989). Cell walls also are involved in water balance, ion exchange, cell ResumenLa lignina es un polímero formado de monolignoles derivados de la vía fenilpropanoide de las plantas vasculares. Se deposita en las paredes celulares de las plantas como parte del proceso de maduración de la célula. En los forrajes, la lignina se considera como un compone...