Chitin and chitosan are naturally occurring biopolymers, which are found in sources such as crustacean shells, cell walls of fungi, and insect exoskeletons. Chitin and chitosan have gained significant interest due to their excellent physicochemical properties, biocompatibility, and biodegradability. Advances in chemical and enzyme tailoring have led to diverse derivatives, expanding their applications in various biofunctions. This chapter explores the origin, structure, and key properties of chitin, chitosan, and their modified forms. It brings to the fore the utilization of such material in some of the fields in which it is found, such as in biomedicine, agriculture, environmental science, the food industry, and industrial processes. Chitosan-based systems are important for wound healing, drug delivery, antimicrobial coatings, biosensors, water treatment, and biodegradable packaging. This chapter reviews advancements in nano-structured and smart chitosan systems, along with regulatory challenges and future prospects for sustainable materials. Overall, it highlights how chitin and chitosan are driving innovation in green and functional material science.