Abstract: Lignin, a complicated organic polymer, plays a significant structural function in the support tissues of vascular plants. It is particularly prevalent in woody plants and is highly polymerized. Lignin is one of the three crucial elements of wood, along with extractives and carbohydrates. Lignin, a three-dimensional amorphous polymer made of methoxylated phenylpropane structures, is important for the survival of vascular plants. In nature, lignin polymer generally forms ether or ester linkages with hemicellulose which is also connected with cellulose. The structural and chemical composition of lignin; representative linkages in lignin molecules and types of lignin are presented in this chapter.