Alginate is a nonrepeating copolymer of b-D-mannuronic acid (M) and a-L-guluronic acid (G), linked by 1–4 linkages. Alginates adopt in nature various material properties ranging from slimy and viscous solutions to pseudoplastic materials when cross-linked with divalent cations. The comonomers are arranged in blocks of continuous M-residues (M-blocks), G-residues (G-blocks), or alternating residues (MG-blocks) (Fig. 1). Alginates are produced by bacteria and brown seaweeds. The M-residues of only the bacterial alginates are acetylated to a variable extent at positions O-2 and=or O-3. The variability in comonomer blocks and the acetylation degree strongly affect the material properties of the polymer. To understand how biological systems control this variability is of scientific and applied importance. Moreover, the analysis and understanding of the structure–function relationships of alginates would provide the basis for the production of tailor-made polymers with particular material properties for a certain application.