Nanocellulose is a biodegradable, renewable, nonmeltable polymeric material that is insoluble in most solvents due to hydrogen bonding and crystallinity. Nanocellulose has attracted considerable attention in recent decades owing to its environmental friendliness, wide availability, good biocompatibility, high crystallinity, and high Young's modulus. This review presents the recent achievements in preparation and applications of nanocellulose, including a discussion of the advantages and disadvantages of various preparation methods and a summary of the applications of nanocellulose in composite materials research. Finally, we examine the mounting evidence of more widespread potential applications of nanocellulose.