Chitin and chitosan, marine polysaccharides with abundant biomass, are gaining attention due to their unique biological and physicochemical properties. This review discusses their preparation, crystallography, N-acetylation, and properties, as well as recent chemical modifications such as acylation, alkylation, Schiff base formation, and sulfation. These modifications enable the creation of sophisticated molecular structures, enhancing their potential for biomedical and biotechnological applications. Chitin, primarily found in arthropod exoskeletons, is abundant in marine crustacean shells, which are a major source. Chitosan, its deacetylated form, is also gaining attention for its non-toxic, film-forming, and adsorption properties. Despite being a common material, chitin has been underutilized due to its complex isolation process. However, recent studies have highlighted its potential as a biofunctional polymer with applications in biomedical fields. Chitin and chitosan are considered environmentally friendly and have unique properties that make them suitable for various applications. Their chemical modification allows for the development of new materials with tailored properties. The review emphasizes the importance of understanding their structure-property relationships and the potential for novel intelligent materials. The preparation of chitin and chitosan involves extracting them from various sources, including marine crustaceans, fungi, and insects. The chemical modification of these biopolymers is a key area of research, aiming to enhance their functionality and expand their applications. The review also highlights the growing interest in these materials and the compilation of research into handbooks for practical applications.Chitin and chitosan, marine polysaccharides with abundant biomass, are gaining attention due to their unique biological and physicochemical properties. This review discusses their preparation, crystallography, N-acetylation, and properties, as well as recent chemical modifications such as acylation, alkylation, Schiff base formation, and sulfation. These modifications enable the creation of sophisticated molecular structures, enhancing their potential for biomedical and biotechnological applications. Chitin, primarily found in arthropod exoskeletons, is abundant in marine crustacean shells, which are a major source. Chitosan, its deacetylated form, is also gaining attention for its non-toxic, film-forming, and adsorption properties. Despite being a common material, chitin has been underutilized due to its complex isolation process. However, recent studies have highlighted its potential as a biofunctional polymer with applications in biomedical fields. Chitin and chitosan are considered environmentally friendly and have unique properties that make them suitable for various applications. Their chemical modification allows for the development of new materials with tailored properties. The review emphasizes the importance of understanding their structure-property relationships and the potential for novel intelligent materials. The preparation of chitin and chitosan involves extracting them from various sources, including marine crustaceans, fungi, and insects. The chemical modification of these biopolymers is a key area of research, aiming to enhance their functionality and expand their applications. The review also highlights the growing interest in these materials and the compilation of research into handbooks for practical applications.