Multiscale Structural Mechanics provides a unified approach for composites modelling based on the representative structure element. After introducing the basic knowledge in vectors and tensors, continuum mechanics, micromechanics and structural mechanics, this concept is introduced and applied to construct micromechanics models and structural mechanics for beams, plates, and shells. This book fills the gap of rigorously bridging micromechanics and structural mechanics. The structural models remain the same as simple engineering models, however with the accuracy comparable to more complex theories. A general-purpose constitutive modelling code also accompanies the book to provide practical tools for engineers to efficiently and accurately model composites.