Polysaccharides are carbohydrate polymers in which monosaccharide ((CH2O)n) units are covalently joined by an O-glycosidic bond in either a linear or branched configuration. Polysaccharides serve as storage of energy, as in starch (unbranched amylose and branched amylopectin) or in glycogen (highly branched molecule), and as a structural component, as in plant cellulose (linear polysaccharide of glucose), bacterial cell walls or agar of seaweeds. Radiation technology offers versatile tools that have an important role to play in support of sustainable development. Ionizing radiation is sufficiently strong to break molecular bonds, creating ions from otherwise stable substances. Being so, ionizing irradiation coming from gamma sources or electron beam accelerators, is one of the available physical methods that can be employed industrially. Radiation technology is used to modify many kinds of materials, changing some properties, many of which can be used in a wide variety of commercial application. Natural polysaccharides can be either degraded or cross-linked by radiation. In this chapter, the focus will be on the interaction of ionizing radiation with polysaccharides and extracellular polymeric substances.