Composites and adhesively bonded structures have many advantages over conventional aircraft materials and constru ction methods, particularly in primary structures. These advantages include a high specific strength and stiffness, formability and a comparative resistance to fatigue cracking and corrosion. However, not forsaking these advantages, these materials and construction methods are prone to a wide range of defects and damage, which can significantly reduce the residual strength of the components. In this chapter is a review of the types of defects and damage found in composite structures, their failure modes and mechanisms, and a general representation of the defect.