This textbook provides readers with the fundamental concepts that underlie the study of any problem of structural mechanics in the linear elastic field. The first part is devoted to the analysis of plane assemblages of beams (including frames, which are widely used in various fields of engineering); the problem of buckling of compressed bars is also dealt with. The second part is devoted to three-dimensional solids of any shape, with particular emphasis on beam-like solids subjected to any combination of external loads. The main criteria used in the Allowable Stress Design method for 3D solids are presented. The book is especially conceived for students of various engineering courses, such as civil, building, mechanical and aerospace engineering.