Rapidly varying material and geometrical characteristics of composite materials and structures do not allow the direct study of their mechanical behavior even with the use of modern computers. This book is devoted to the mechanical design and optimization problems of composite structures, based on the previously developed asymptotic homogenization models and on the newly elaborated rigorous mathematical methods. It describes how to construct mathematically rigorous mechanical models to determine strength, stiffness, and weight minimization requirements, all important factors of design and optimization.