This text explores two-dimensional lattice models in statistical mechanics and illustrates methods for their solution. Comprehensive but concise, it indicates the routes between equations without superfluous details. Author R. J. Baxter is a fellow of the Royal Society of London and the Australian Academy of Science, as well as Emeritus Professor of the Mathematical Sciences Institute at Australian National University, Canberra. Professor Baxter has updated this edition with a new chapter covering recent developments. Starting with a survey of basic statistical mechanics, the treatment proceeds to examinations of the one-dimensional Ising model, the mean field model, the Ising model on the Bethe lattice, and the spherical model. Subsequent chapters address duality and star-triangle transforms of planar Ising models, the square-lattice Ising model, ice-type models, and the square lattice eight-vertex model. Additional topics include the Kagomé lattice eight-vertex model, Potts and Ashkin-Teller models, Corner transfer matrices, hard hexagon and related models, and elliptic functions. Seventy-six figures illuminate the text.