Understanding the fracture behavior of composite materials is essential for ensuring the safety and reliability of primary structures that have applications in industries. This chapter provides a comprehensive overview of the application of fracture mechanics to composite materials when subjected to both modes I and II, as well as the mixed-mode loading conditions. This assessment begins by presenting the fundamental principles of fracture mechanics and their applicability to composite materials. It explores the unique challenges associated with predicting the remaining fatigue life of composites, considering factors such as anisotropic nature of material, fiber orientation, matrix properties, and environmental conditions. The role of manufacturing processes and defects in influencing fatigue and fracture is also discussed, highlighting the need for quality control and proper nondestructive inspection methods. This work also discusses experimental techniques and testing procedures for obtaining the fracture toughness and fatigue crack growth rate data of composite parts subjected to both mode I and II. These data can be utilized in estimating the number of cycles to failure when components are exposed to cyclic load environments. It explores the applicability of linear elastic fracture mechanics in assessing fracture behavior of composite structures. Furthermore, several scenarios concerning crack behavior were assessed. Crack growth in the matrix, when defects are parallel and perpendicular to the fibers under mode I is discussed. The case of crack arrest at the interface, the bridging mechanisms where fibers are untouched, and the presence of defects because of delamination are also presented in this chapter. It further discusses ongoing research efforts aimed at improving prediction accuracy, the question of which parameter should be used when plotting fatigue crack growth results, developing standardized testing procedures, and advancing the understanding of the complex interactions between various factors influencing fatigue crack/damage growth behavior in composites under mode I, and II, as well as mixed-mode loading conditions.