This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book deals with the frequency analysis of buildings. Closed-form formulae and tables make it possible to calculate the lateral and torsional frequencies of the building. The book introduces the global critical load ratio which is a useful tool for monitoring the “health” of the bracing system. The examples range from the deflection or frequency or stability analysis of individual bracing units to the complex deflection and frequency and stability analyses of bracing systems, considering both planar and spatial behaviour. The global critical load ratio can also be used to assess different bracing system arrangements in order to choose the most economic one. The results of several comprehensive worked examples demonstrate the practical use of the global critical load ratio.