Drilling is the most common machining process in the manufacture of components and structures from composite materials. Conventional drilling with a twist drill is widely adopted for this. However, it is difficult to ensure proper hole quality on composites due to their special characteristics. Special drill bits, in terms of their geometry and material and nonconventional hole-making processes have been developed to improve the quality of drilled holes in composites. Delamination is the major drilling defect that causes failure of composite structures. The severity of delamination damage is assessed by various measures or delamination factors. There are delamination suppression techniques that have been developed for different drilling applications.