Three efficient and straightforward chemical pathways have been studied to functionalize solid cellulose substrates, involving for the first time alkoxysilane chemistry coupled with the photochemical version of the thiol-ene reaction. The success of the reactions was confirmed using FTIR-ATRspectroscopy and XPS analysis, but different grafting efficiencies were observed depending on the combination used. In a first route, ene-functionalized cellulose films were synthesized using vinyltrimethoxysilane as coupling agent, and were photochemically coupled with methylthioglycolate (MeGlySH). A very fast reaction rate was observed for this reaction during the first 5 min. In a second route, the opposite reaction was envisaged by clicking allylbutyrate on a thiol-functionalized cellulose surface, previously synthesized using 3-mercaptopryltrimethoxysilane as coupling agent. The success of the reaction was highlighted, but lower modification rates were observed. In a third route, a novel approach was successfully proposed for the grafting of thiol molecules on cellulose, based on the click derivatization of the molecule with alkoxysilane functions. Through this study, we expand the modular and versatile character of click chemistry to natural cellulosic substrates. But most importantly, these modification routes can be envisaged for the functionalization of other surfaces (i.e., metal alkoxides for instance) where alkoxysilane chemistry can be employed.