Nanocellulose has generated a great deal of interest as a source of nanometer-sized reinforcement, because of its good mechanical properties. In the last few years, nanocellulose has also attracted much attention due to environmental concerns. This review presents an overview of recent developments in this area, including the production, characterization, properties, and range of applications of nanocellulose-based biodegradable polymers, thermoplastic polymers, and porous nanocomposites. After explaining the unique properties of nanocellulose and its various preparation techniques, an orderly introduction of various nanocellulose-reinforced biodegradable polymers such as starch, proteins, alginate, chitosan, and gelatin is provided. Subsequently, the effects of nanocellulose on the properties of thermoplastic polymers such as polyamides, polysulfone, polypropyrol, and polyacronitril are reported. The paper concludes with a presentation of new finding and cutting-edge studies on nanocellulose foam and aerogel composites. Three different types of aerogels, i.e., pristine nanocellulose-based aerogels, modified nanocellulose-based aerogels, and nanocellulose-based templates for aerogels, are discussed, as well as their preparation techniques and properties. In the case of foam composites, the research focus has been on two major preparation techniques, i.e., solvent-mixing/foaming and melt-mixing foaming, their respective challenges, and the properties of the final composites. In some cases, a comparison study between cellulose nanocrystals and cellulose nanofiber-reinforced biodegradable polymers, thermoplastics, and porous nanocomposites was carried out. Considering the vast amount of research on nanocellulose-based composites, special emphasis on such composites isprovided at the end of the review.