Abstract: The latest research progress of interleaving of fibre-reinforced thermoset polymer matrix composite (PMC) is reviewed. Thermoset composites are brittle due to the high crosslink density of the matrix resin, which exhibit low impact damage resistance and damage tolerance. Interleaving of the flexible polymer improves interlaminar fracture toughness and damage resistance without sacrificing the excellent thermal properties and high modulus of the thermosets.There are three types of interleaving methods which seem to be the most frequently reported methods, namely particle, polymer fiber and polymer film interleaving. The concept, implementary methods, toughening mechanism and research results are discussed. Finally, the emphasis on interleaving composites by innovative ex-situ concept is putted. Ex-situ high-performance technology system for composites with intellectual property consisting of prepreg-based and liquid molding composites are introduced.