Book excerpt: "The aim of this book is to construct harmonic maps between Riemannian manifolds, and in particular between spheres. These maps have a delightful geometry associated with them - they preserve families of level hypersurfaces of constant mean curvature. New maps between Euclidean spheres are constructed, as well as harmonic maps from hyperbolic space to sphere and from Euclidean space to sphere. The author makes considerable use of the stress-energy tensor, which has not previously been used in the context of harmonic maps...In particular, it is used to solve the rendering problem for certain classes of maps between spheres." - back cover