Following the advent of nanotechnology and the growing interest dedicated to the exploration of the many properties attributed to nanoparticles, bionanocrystals derived from natural polysaccharides have also attracted great attention owing to their distinct biocompatibility and biodegradability along with their wide availability and attractiveness as renewable biomasses. Among this class of bionanoparticles, cellulose (CNCs) and chitin (ChNCs) nanocrytals (the two most abundant natural polymers on earth), have emerged in the development of a wide range of applications in the field of materials science, and in recent years also in tissue engineering (TE) and regenerative medicine. In these chapter we overview the latest advances on the use of these outstanding natural build block in the development of functional nanostructured biomaterials for potential TE applications and highlight their main properties to be explored within the field.