In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. Typical fiber reinforcements include glass, carbon, Kevlar, and boron.
Epoxies are also used as a structural glue. Materials like wood, and others that are 'low-tech' are glued with epoxy resin. One example would be the RJ.03 IBIS homebuilt canard aircraft. This design is based on a classic wooden lattice structured fuselage and a classic wooden spar, internally stiffened with foam and completely covered with plywood. Except for the plywood covering the wings, everything is glued with epoxy resin.