This book is written by a group of researchers based on the recent research progress in the fiber/matrix interface degradation under various environmental exposures via molecular dynamics simulation. It provides systematic framework of the model development, simulation techniques, and simulation results and presents the future research directions for investigating the interfacial degradation. By introducing the molecular details of fiber/matrix interface under environmental effects, it advances the fundamental understanding of the interfacial degradation mechanism. Researchers, scientists and engineers in the field of civil engineering and composite materials can benefit from the book. In conclusion, this book provides a computational paradigm and valuable insights on the fundamental interfacial degradation mechanism, which can contribute to the prediction of long-term behavior of fiber-reinforced polymer composites in harsh environments and pave the way for the material design with stronger interface.