Abstract: A lightning resistant composite structure, particularly for aircraft, in which a composite skin panel, for example of carbon fibre, is attached to an inner composite structure by one or more lightning resistant fastener assemblies. The fastener assembly comprises a nut and bolt, the bolt being in good conductive contact with a conductive sleeve engaging the skin panel and a non-conductive sleeve engaging the inner structure. The nut is contained within a capped nut assembly located to the undersurface of the inner structure.The non-conductive sleeve and the capped nut assembly isolate the inner structure from the effects of lightning strike, the conductive sleeve providing a high quality conductive interface between the bolt and the skin panel. By this means adverse penetration of lightning current into the inner structure is prevented.