AbstractChitosan is a natural polycationic polymer which possesses valuable properties as a metal recovering and water purifying agent. Applications are—waste water treatment for heavy metal and radio isotope removal and valuable metal recovery,—potable water purification for reduction of unwanted metals,—agriculture—controlled release of trace metals essential to plant growth,—food—complex binding of iron in precooked food to reduce ‘warmed‐over flavour’.The interactions of metals with chitosan are complex, probably simultaneously dominated by adsorption, ion‐exchange and chelation. To study this it is of utmost importance to work with well characterized chitosans. This has been a problem as available characterizing methodology is limited.Degree of polymerization and deacetylation and the distribution of acetyl groups along the polymer chain is of crucial importance for chitosan metal interacting characteristics. Making chemical derivatives is a way to alter the metal interacting characteristics of chitosan.Chitosan possesses general coagulant/flocculant characteristics towards bio‐molecules and surfaces.