Due to the unique optical, mechanical, and thermomechanical properties of cellulose nanomaterials, the two most common types being cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), there is a growing interest to incorporate them into advanced materials, ranging from nanocomposites to medical devices, biosensors, Pickering emulsions and foams, and organic electronics. However, the hydrophilic and hygroscopic nature of cellulose nanomaterials limits or even hinders their incorporation into hydrophobic matrices, thus surface modification by means of physisorption of surface-active compounds or covalent functionalization with small molecules or polymers by “grafting to” or “grafting from” methods offers tools to tailor their interfacial properties. In this chapter, we provide an overview of the various means to modify the surface nanocellulose substrates, especially those derived from lignocellulosic raw materials. Surface modification methods will include those through physical, chemical, and enzymatic means to tailor nanocellulose interfacial properties.