Irregular engineering structures are subjected to complicated additional loads which are often beyond conventional design models developed for traditional, simplified plane models. This book covers detailed research and recent progress in seismic engineering dealing with seismic behaviour of irregular and set-back engineering structures. Experimental results as well as special topics of modern design are discussed in detail. In addition, recent progress in seismology, wave propagation and seismic engineering, which provides novel, modern modelling of complex seismic loads, is reported. Particular emphasis is placed on the newly developed rotational, seismic ground-motion effects.