Composite materials have many advantages over conventional structural materials, particularly in primary structure. The advantages of composite materials include a high specific strength and stiffness, formability, and a comparative resistance to fatigue cracking and corrosion. The damage can significantly reduce the residual strength and stiffness of the structure or result in unfavourable load paths. When the damage is found in the composite structure, the next step is to determine the loss of structural or performance integrity. The material is generally more susceptible to defects and damage from the operational environment. The resulting structure provides an increase in the damage tolerance and toughness of the brittle fibres, with minimal loss of the beneficial mechanical and physical properties of the fibres. The repair of composite structures requires more than just the physical repair action. The chapter also presents an overview of the key concepts discussed in this book.