The function spaces discussed in this book are the natural ones in which to look for solutions of Partial Differential Equations and of problems in the Calculus of Variations (and so I don't think the material is esoteric!). This book is simply necessary for analysts and for anyone interested in rigor in the context of PDE. It is not as readable as the book by Evans and Gariepy, which is a pleasure to read cover to cover, but it contains more information and discusses some more technical spaces.
