Recently, nanocelluloses have gained great interest as naturally derived biobased nanometer-sized reinforcement in diverse technological areas due to the excellent mechanical properties, biodegradability, biocompatibility, high specific surface area, and rich hydroxyl groups for extensive chemical modification. However, the extraction of nanocellulose from cellulosic biomass and its dispersion in the matrix is still a substantial challenge since its inherent hydrophilicity and difficulty in dispersion inside hydrophobic matrix. This paper presents an overview of recent developments in nanocellulose research, highlighting its extraction routes, surface modification and its applications in polymeric composites. Literature shows that the morphologies and performances of nanocellulose depends on the source of the cellulosic materials and the processing parameters. Although nanocellulose is derived from seemingly fragile plants or organisms, it can be used as the reinforcement material or the main component to fabricate high value-added cutting-edge materials or devices, such high-performance nanocomposites, multifunctional hydrogel, conductive filaments, medical dressing, and energy storage material.