In this paper chitin and chitosan were considered copolymers of N-acetyl-D-glucosamine and D-glucosamine, linked by covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). As a consequence their thermal behaviour as well as the mechanical properties of chitosan films could be correlated to their copolymeric structure (amount and distribution of the two comonomers in the biopolymeric chain).