Chitosan is an emblematic example of biopolymer that can be obtained from renewable resources (fungal biomass, crustacean shells…) and that can be used for binding a number of metal ions through different mechanisms (complexation, electrostatic attraction, ion pair formation). Chitosan was used for the sorption of various transition metals, from toxic (Hg(II), Cd(II), U(VI), Mo(VI), V(IV) and V(V) …) to strategic and valuable metals (Pd(II), Pt(IV), Au(III) …). However, the interactions of chitosan with metal ions are not strictly limited to environmental applications. Hence, the binding of metal ions on the biopolymer can be used for designing new materials or new applications. Some examples are reported below.