Green chemical modification of cellulose presents a unique challenge, particularly from the perspective of sustainable development. Many strategies commonly used in polymer chemistry cannot be directly transposed to this essential biopolymer in the search for alternatives to fossil-based materials. The absence of simple and environmentally friendly solvents for cellulose processing forces us to change our paradigm. A more desirable strategy would involve working under heterogeneous conditions, utilizing readily available cellulose sources, such as wood or wood fibers, that do not require extensive processing and, of course, use non-hazardous reactants and solvents of biobased relevance. This framework has been the guiding principle of this PhD project, which first focused on developing a novel bio-based reactivity promoter for heterogeneous reactions (improving chemical accessibility of cellulose). [1] The methodology was then further extended to other relevant bio-based anhydrides. [2] Finally, fine-tuning cellulose chemistry through this approach enabled us to explore new material design concepts, ranging from ultra-charged fibers for water remediation to innovative, high-strength wood plastics.