Chitin and chitosan, marine polysaccharides, are gaining significant attention due to their unique biological and physicochemical properties. This review covers the fundamental aspects of chitin and chitosan, including their preparation, crystallography, N-acetylation, and properties. Recent advancements in their chemistry, such as chemical modifications like acylation, alkylation, and sulfation, are also discussed. Chitin and chitosan, abundant in marine crustacean shells, have been underutilized until recently, when their potential as biofunctional polymers became better understood. These polymers exhibit non-toxicity, film- and fiber-forming properties, metal ion adsorption, and biological activities, making them promising for various biotechnological applications. The review highlights the importance of these polymers as environmentally friendly resources and the ongoing research into their chemical modifications to explore their full potential.Chitin and chitosan, marine polysaccharides, are gaining significant attention due to their unique biological and physicochemical properties. This review covers the fundamental aspects of chitin and chitosan, including their preparation, crystallography, N-acetylation, and properties. Recent advancements in their chemistry, such as chemical modifications like acylation, alkylation, and sulfation, are also discussed. Chitin and chitosan, abundant in marine crustacean shells, have been underutilized until recently, when their potential as biofunctional polymers became better understood. These polymers exhibit non-toxicity, film- and fiber-forming properties, metal ion adsorption, and biological activities, making them promising for various biotechnological applications. The review highlights the importance of these polymers as environmentally friendly resources and the ongoing research into their chemical modifications to explore their full potential.