Lignin, a complex and plentiful biopolymer sourced from lignocellulosic biomass, has attracted considerable attention as a renewable resource for the development of sustainable materials. Among the various chemical modification techniques, epoxidation is particularly notable for its ability to enhance the reactivity and functionality of lignin for advanced applications. This chapter explores lignin functionalization via epoxidation, including its chemistry, methods, and resulting properties. The chapter examines epoxidation mechanisms, focusing on reaction pathways and the roles of key reagents and catalysts. Furthermore, it discusses characterization methods such as FTIR, NMR, and TGA, which confirm the structural, thermal, and morphological alterations in lignin following epoxidation. The potential applications of epoxidized lignin in polymer composites, coatings, and adhesives are emphasized, illustrating its capability to substitute petroleum-based precursors and aid in the creation of biobased materials. Lastly, the chapter addresses challenges related to the scalability of reactions and the uniformity of functionalization, while also outlining future research directions focused on optimizing eco-friendly epoxidation processes and broadening the applications of lignin in high-performance materials.