In practice, the problems connected with the fatigue of composites are intricate because of their complex structure and the fatigue loading. Fatigue tests under different fiber orientation angles are time-consuming and also very expensive. Therefore, it is important to establish a technique to consider the fatigue damage at any fiber orientation angle without having to perform excessive amounts of testing. The general purpose is to elaborate a methodology for finding a globally optimum design of composite laminates subjected to in-plane loads. In this part of the study, the Fawaz-Ellyin model of fatigue life prediction is presented and further validated. The results obtained show that the model can be applied to optimization problems of composites.