This book introduces an analytical method, the U-transformation method, for the exact analysis of structures with the periodic property. The physical meaning of U-transformation is fully explained and the application of this technique to derive exact analytical solutions for a wide variety of structures with the periodic property is thoroughly illustrated. The book also provides useful exact and explicit formulas for many practical engineering problems. Many of these solutions are new results that have just appeared in international journals. The practical engineering structures considered in the book include continuous beams, stiffened plates, trusses, grillages, double layer grids and so on.