This chapter is an introduction to the rheology of epoxies and rubbers, their blends, classification, and types. Principles of rheology and polymer rheology are illustrated through conclusive plots and graphs. Rheology of rubbers, epoxies, and their blends are discussed with respect to their molecular structure, mobility, and conformational states. Rheology is explained with respect to the established viscoelasticity models for epoxies and their blends. A detailed account of rheometers and measurements is given. Miscibility, phase separation, and thermodynamics of epoxy-rubber systems form an integral part of this chapter. A correlation is drawn between rheology and shear behavior of these systems. Rheological insights on processing, manufacturing methods, curing reactions, and curing schedules are detailed for epoxy-rubber blend systems. Functional and product applications of rheology of epoxy/rubber blends are listed at the end.