Wood templates are promising biobased substrates that can be functionalized for controlled nanostructure, and the development of novel nanotechnologies. A sustainable, selective and versatile chemical functionalization platform for cellulosic wood templates is developed. Bulk wood templates are delignified using peracetic acid, and the nanoporous delignified wood templates are functionalized with cyclic anhydrides (maleic, itaconic and succinic) from renewable resources. The synthetic pathway uses solvent-free reaction conditions, short reaction times, and has possibilities for chemical recovery. Anhydrides become covalently attached inside the nanoporous wood cell wall and yields wood templates with lower moisture sorption, preserved nano- and ultrastructure, and high degree of esterification with carboxyl content as high as 3.93 mmol g−1. The functionalization platform enables interface tailoring at the molecular scale with possibility for further reaction and covalent modifications. This is demonstrated by the preparation of transparent wood biocomposites. The biocomposites exhibit controlled wood–polymer interfacial adhesion with high optical transmittance. The favorable interaction mechanisms at the cell wall level result in mechanically strong biocomposites.