This book describes the stress and deformations of solid bodies in contact with each other, along curved surfaces which touch initially at a point of contact or along a line. Examples are a railway track and the wheels running in it, or a pair of meshed gear teeth. The book commences with the development of the theory since the problem was first described in 1882. Next there is a discussion of the influence of friction and the topographical roughness of surfaces, and this is built into the theory. An important feature of the text is the treatment of plastic and viscoelastic bodies. An appreciable section of the book is on bodies in sliding or rolling contact. The mathematical treatment assumes that users of the book are graduates in engineering; it is a book written by a distinguished engineer for other professionals and their graduate students.