The subject of this chapter is applications of electron beam radiation in processing and modifications of polymers, monomers, and oligomers. The advantages of electron beam radiation, which is an ionizing radiation, are clean and safe technology, the almost instant conversion, and excellent control of dosage and penetration depth of the beam of accelerated electrons. It is used in a variety of industrial applications such as wire and cable insulations; tire manufacturing; production of polymeric foams, heat-shrinkable films, and tubings; curing of coatings, paints, and adhesives; printing as well as in curing of composites and hydrogels. Electron beam radiations works well in cross-linking, grafting, and modification of most solid polymers (thermoplastics and elastomers) and in polymerization of many monomers and oligomers.