Manufacturing defects are inevitable in composite structures. They can be reduced but not totally eliminated. While the defects depend on the manufacturing process, their significance varies with the performance requirements placed on the structure. A good engineering approach is, therefore, to allow defects that would not jeopardize safe performance and in return reduce the manufacturing cost. This chapter reviews common manufacturing defects in composites followed by discussions of their effects on performance and implication on cost reduction by cost/performance trade-offs.