Much of our theoretical understanding of phase transitions is based on the two-dimensional Ising model. Barry McCoy and Tai Tsun Wu clearly show that new techniques have been developed resulting in considerable simplification of the model. They discuss not only spin-correlation functions of the model but also a quantitative study of the influence of impurities on phase transitions. To keep that starting point as elementary as possible, the authors provide all the statistical mechanics needed for the entire book in the first chapter.