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Microbial polysaccharides are high molecular weight (Mw) carbohydrate polymers produced by microorganisms, namely, bacteria, fungi, yeast, and microalgae [1,3]. They include intracellular polysaccharides that are accumulated in the cytoplasm of the cells as carbon and energy reserves (e.g. glycogen), cell‐wall polysaccharides that contribute to the cells' structural stability (e.g. chitin), and extracellular polysaccharides that are secreted by the cells, forming either a capsule that remains associated with the cell surface (capsular polysaccharides [CPS]) or a slime that is loosely bound to the cell surface (exopolysaccharides [EPS]) [2,4]. Of the last type, CPS are mostly associated with the pathogenicity of bacteria and virulence‐promoting factors [5], while EPS have been proposed to provide protection against environmental stress, cell adherence to surfaces, and carbon or water storage reserves [6].

Polysaccharides can be used into two main areas of application: (i) as structuring agents, based on their ability to form polymeric structures, such as films, gels, emulsions, microparticles, and nanoparticles, and (ii) as biological active materials/compounds that can be used for the development of novel pharmaceutical drugs or replace some of the currently used products [7,8]. Other applications include their use as sources of high‐value monomers, such as rare sugars (e.g. fucose, rhamnose, ribose, glucuronic acid, etc.), to generate oligosaccharides (e.g. galactooligosaccharides, fucooligosaccharides) that can be used in nutraceuticals [9].

This chapter starts with a brief overview on microbial polysaccharide diversity in terms of functional properties and their main areas of application (Section 2.2), followed by a more detailed analysis of the currently more relevant and emerging areas (Sections 2.3–2.7).