Nanocellulose, a versatile green material derived from natural sources, has gained significant attention due to its renewability, abundance, and unique properties. This review covers the sourcing, synthesis, surface modification, and applications of nanocellulose-based materials. Nanocellulose can be extracted from biomass, plants, or bacteria using mechanical, chemical, or enzymatic treatments. Surface modifications, such as phosphorylation, carboxymethylation, and sulfonation, enhance the functionality and properties of nanocellulose. Nanocellulose exhibits excellent mechanical strength, biocompatibility, and tunable self-assembly, making it suitable for a wide range of applications, including functional paper, optoelectronics, antibacterial coatings, packaging, polymer composites, tissue scaffolds, drug delivery, biosensors, energy storage, catalysis, environmental remediation, and electrochemical separation. The review also highlights the potential of phosphorylated nanocellulose in applications such as bone scaffolds, adsorbents, flame retardants, and catalyst supports.Nanocellulose, a versatile green material derived from natural sources, has gained significant attention due to its renewability, abundance, and unique properties. This review covers the sourcing, synthesis, surface modification, and applications of nanocellulose-based materials. Nanocellulose can be extracted from biomass, plants, or bacteria using mechanical, chemical, or enzymatic treatments. Surface modifications, such as phosphorylation, carboxymethylation, and sulfonation, enhance the functionality and properties of nanocellulose. Nanocellulose exhibits excellent mechanical strength, biocompatibility, and tunable self-assembly, making it suitable for a wide range of applications, including functional paper, optoelectronics, antibacterial coatings, packaging, polymer composites, tissue scaffolds, drug delivery, biosensors, energy storage, catalysis, environmental remediation, and electrochemical separation. The review also highlights the potential of phosphorylated nanocellulose in applications such as bone scaffolds, adsorbents, flame retardants, and catalyst supports.