Nowadays, the incremental demands on utilization of renewable biomass has emphasize the importance of cellulosic materials. This can be justified by the large number of publications as well as the new generation of materials made from biosource residues. Cellulosic fibers present many potential advantages: the most important of them are their bio-renewable character, their ubiquitous availability in a variety of sources, and their low cost. This chapter presents a general overview of the preparation and characterization of nanocellulose from various sources. These products have recently acknowledged considerable attention as a potential source to produce nanomaterials with higher excellent performances. The preparation and characterization of cellulose nanocrystals (CNC), nanofibrillated cellulose (CNF), and bacterial nanocellulose (BNC) were discussed.