This chapter examines the following concepts: overview of epoxy and its uses, structure of the polymer, cross-linking and processing parameters, physical and mechanical properties of cured epoxy composites,and special composite applications (prepregs tooling). Epoxies are the second most widely used family of thermosetting resins for composite applications (after polyester thermosets). In contrast to the polyester thermosets, about 50% of all epoxy resins are used for non-reinforced applications. Most epoxies are cured at elevated temperatures to facilitate the movement of the resins and hardeners, thus increasing the likelihood of their colliding and resulting in a cross-linking reaction. Epoxy resins are the second most widely used matrix materials for composites.