lignin is one of the most abundant biopolymers on earth which has recently gained considerable attention due to its unique potentials to be used in many applications. many efforts have been made in improving the compatibility and reactivity of lignin for different applications. although different methods have been suggested to ameliorate lignin properties, there has been a continuous demand for finding effective and new ways of revealing the beneficial uses of this polymer. to address the lack of fundamental understanding of lignin modification pathways in generating lignin-based products, the chemical reactions conducted via grafting functional groups of lignin has been comprehensively reviewed in this thesis. also, the recent progress on lignin reactions as well as advantages and disadvantage, challenges associated with the product development process, and the reaction procedures have been discussed comprehensively in this work. also, from the commercial point of view, products such as vanillin and phenol have been commercially available since 1933 and 2015, respectively, with equal or lower prices to their fossil-based counterparts. lignin-based carbon fiber is also estimated to be produced commercially in 2020-2025. overall, by reviewing different reactions performed on lignin in this chapter and revealing the possible ones that could be implemented, lignin-based polymers with improved properties could be generated to pave the way to even more commercial products from lignin.