Chitosan surface properties comprise the physicochemical characteristics expressed at the outermost region of chitosan polymers, films, coatings, and interfaces, together with their dependence on molecular structure and surrounding conditions. They include surface chemical composition and functional-group availability, wettability, surface free energy, polarity, charge, roughness and topography, swelling, hydration, and interfacial adhesion. These properties arise primarily from the distribution and protonation of amino groups, hydroxyl groups, acetylated units, and associated water or counterions, and are influenced by the degree of deacetylation, molecular weight, crystallinity, film-formation method, pH, ionic strength, and surface treatment ^[1][2][3]. In aqueous acidic environments, protonation of amino groups gives chitosan cationic interfacial behavior, whereas changes in pH and ionic composition can alter hydration, conformation, cohesion, and interactions with adjacent surfaces ^[1]. The term therefore concerns properties localized at or governing the polymer interface; it is distinct from bulk mechanical, thermal, or biodegradation properties except where those characteristics modify the exposed surface or its interfacial response ^[2][3].