The crack healing by hollow fibre delivery of chemical adhesives, along with the recently formulated concept of self-healing smart composites, is reviewed in this paper. The latter, whereby the procedure of microcapsules induced crack self-healing, is thoroughly investigated. Discussion comprises a number of topics including the structures of healing agents and catalysts employed, microcapsule forming and exterior attachments with a catalyst, in-situ polymerisation kinetics, crack self-healing in neat epoxy and composites, healing efficiency and microscopes of healed composites. A typical dual phase self-healing system involves microencapsulated dicyclopentadiene (DCPD) performing ring-opening metathesis polymerization (ROMP) under an embedded Ru catalyst complex within an epoxy matrix. For neat epoxy resin the healing efficiency is as high as 90% at ambient temperature, while for carbon fabric reinforced composites it is approximately 45% at room temperature and up to 80% at 80℃. Norbornene (NB) and its derivates have a similar self-healing function. An un-catalysed thermal reversible reaction of a multi-furan and multi-maleimide can form endless re-mendable cross-linked polymerization to heal cracks automatically. A comparison of the characteristics of various self-healing agent systems and composites are proposed.