Nanocellulose is emerging as an important material given the abundance of cellulose, properties such as high specific surface area, inherent fibrous morphology, biocompatibility, and most importantly, awide variety of methods available to obtain it. Cellulose is isolated from numerous sources including plants, trees, tunicates, and bacteria. The properties of nanocellulose mainly depend on fabrication route, processing conditions, and the source of cellulose. Cellulose isahierarchical organization of polyglucan chains that assemble into semicrystalline fibers and bundles. This chapter provides insights into two significant aspects of nanocellulose-nanocellulose production and functionalization. Various nanocellulose fabrication techniques are discussed and categorized into top-down and bottom-up approaches. Further, abrief review of work carried out to functionalize nanocellulose to enhance its functionality, dispersibility, processability, and mechanical integrity is provided. A brief section is also included to discuss scale-up of nanocellulose and existing commercial landscape. © 2022 Elsevier Inc. All rights reserved.