In this chapter, a review of several research on the development and characterization of cellulose, the discussion focuses on structural, mechanical, and cellulose degradation. Nanocellulose has renewability, availability, lightweight, low cost, most importantly minimum environmental impact (Ecofriendly), and little effect on animals and human health. General properties of cellulose include extensive chemical modification capability, very high aspect ratio leading to the formation of versatile semicrystalline fibers which is the unique characteristic of nanomaterials as reinforcing agents. There is a strong and complex network of hydrogen bonds that are stabilized by the ordered regions of cellulose chain packages. It resembles nanocrystalline rods. There are two main types of nanocellulose: (i) nanocrystalline and (ii) microfibrillated cellulose. Different types of plants are the main sources of cellulose, but some sea animals such as tunicates and algae are capable of producing cellulose fibers. Another type of nanocellulose is also known as bacterial cellulose. Specific bacteria mainly Gluconacetobacter strains secrete these cellulose nanofibers extracellularly. Because of their special fibrillary nanostructure, these bacteria have exceptional mechanical and physical properties. Their properties include high-strength crystalline and high-elastic module. Bacterial cellulose is currently the subject of research in several fields of application, reinforcement in nanocomposites, biomedical applications, and fuel cell membranes.