Material behaviors at the macroscale level are controlled by their characteristics at lower-scale levels. This fact is even more significant for composite materials. As a result, in order to design and analyze composite structures as well as new composite materials, it is necessary to model material behaviors at different length scales. This book presents the state of the art in multiscale modeling and simulation techniques for composite materials and structures. It focuses on the structural and functional properties of engineering composites and the sustainable high performance of components and structures. These multiscale techniques can also be applied to nanocomposites. The book provides highly useful information for engineers and materials scientists for designing and analyzing composite structures.