Chitin and chitosan have been receiving great attention as a novel functional material for their excellent biological properties such as biodegradation, immunological, antioxidant and antibacterial activities. However, its use has been scarcely developed due to its high molecular weight, which causes poor water solubility and high viscosity of the solutions. Compared with ordinary chitosan, chitosan oligomers have much improved water-solubility and some special biological functions due to the high absorption rate at the intestinal level, thus permitting its entrance in blood circulation and distribution all over the body. The potential application of chitin and chitosan, and respective oligomers, is multidimensional and it has been found in food and nutrition, biotechnology, material science, drug delivery, agriculture and environmental protection, and recently gene therapy too. In the realm of this chapter, we will focus on some biological activities attributed to those molecules, such as, antimicrobial and antifungal activities, wound healing, antioxidant, anti-inflammatory, anti-carcinogenic and anti-coagulant.