Fiber composites, like metals, exhibit a form of degradation in service described as fatigue. Engineers must understand composite fatigue because it is a causative agent of design and structural failures. Engineers need to increase their knowledge of the mechanisms which result in degradation in order to predict the life of a composite under specified conditions and produce composites with greater durability. This book provides an extensive account of contemporary research on fatigue from a selection of internationally recognized researchers. Part one introduces the concept, delivering a historical review of the fatigue behavior of fiber-reinforced plastics and illustrating fatigue test methods and fatigue under multiaxial stress systems. The second part reviews current research on micromechanical aspects, emphasizing long-term behavior, interface performance, delamination, and damage accumulation. The next two sections cover the analysis and testing of fatigue behavior and detail physical, micromechanical, computational, statistical, and life-prediction models for constant and variable stress. The final parts offer an overview of the wide range of composite fatigue-related problems experienced by engineers in aerospace, marine, and structural engineering.