Nanocellulose (NC) represents a pivotal material for the sustainable strategies of the future. NC comprises cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs), and bacterial nanocellulose (BNC), each exhibiting unique and exceptional physicochemical properties. These properties encompass high specific surface area, high tensile strength, lightweight, biodegradability, good barrier properties, and high processing versatility. However, the range of properties and applications can be significantly expanded through the modification of NC, involving both chemical and physical methodologies, which introduce a plethora of functional groups to the densely populated hydroxyl groups present in pristine NC. The modification processes discussed in this chapter encompass chemical and physical modifications that were reported mostly within the last 5 years. The described methodologies emphasize the potential of NC as a substrate for advanced functional and sustainable materials