The thesis is dedicated to the study of the effects of voids on the mechanical properties of a ±45° unidirectional glass fiber reinforced composite. Voids are a widely studied defect on composite materials, as they are very common and have a significant detrimental effect on the mechanical properties. Also, as their total elimination is a difficult and expensive process, they need to be tolerated and their effects need to be accounted for. The reduction in mechanical properties, such as young’s modulus and ultimate stresses, is due to the fact that, at the voids tip, a stress intensification phenomenon arises, and facilitates the creation of a crack.