Epoxy is a crucial engineered thermosetting polymer with wide industrial applications in adhesive, electronics, aerospace and marine systems. In this review, basic knowledge of epoxy resins and the challenge for the preparation of epoxy nanocomposites are summarized. The state-of-art multifunctional epoxy nanocomposites with magnetic, electrically conductive, thermally conductive, and flame retardant properties of the past few years are critically reviewed with detailed examples. The applications of epoxy nanocomposites in aerospace, automotives, anti-corrosive coatings, and high voltage fields are briefly summarized. This knowledge will have great impact on the field and will facilitate researchers in seeking new functions and applications of epoxy resins in the future.