This chapter investigates the behavior of composites under high-cycle fatigue conditions, aiming to understand and characterize the composite material’s response to repeated cyclic loading. High-cycle fatigue poses unique challenges in composite materials due to their complex structures, with high-strength fibers, a weak matrix, and the interface between the two constituents. The material presented in this chapter employs a comprehensive experimental approach to explore the fatigue behavior of composite materials through conducting numerous stress-to-life test data (S-N) under cyclic loading. The study explores the influence of several parameters on the fatigue behavior of composite materials, such as fiber volume, high-frequency loading, fiber orientation, shape of the cyclic loading, effect of mean stress, effect of notch, effect of continuous and discontinuous fibers, stress ratio, and environmental effects such as moisture, temperature fluctuations, and any possible radiation exposure. All these aspects are discussed in this chapter. Additionally, several empirical models were examined to help engineers minimize the number of S-N tests. Finally, the results of S-N data provided in this work enhance our understanding of the complex relationship between composite structures and cyclic loading, contributing to the advancement of composite materials for applications in aerospace, automotive, and other industries where fatigue resistance is a critical factor.