"The purpose of the book under review is to present perspectives for the development of the theory of spaces that have 'decent calculus' like the spaces supporting Poincaré inequalities. . . .The book is written in a very informal style. There are almost no theorems or proofs, just questions and elaborated comments. One of the features of most of the mathematical books and papers is that the reader is forced to spend hours on checking painful details in order to follow the text. However, a consequence of the informal style of Semmes is that there is no such need here. On the contrary one can enjoy reading the whole book in a couple of evenings without any danger of being exhausted! The purpose of the book is to suggest possible directions of research in the fascinating area of analysis on metric spaces. Everybody doing research in this area should read the book." -- Mathematical Reviews

"[A] rich overview of this recent and fascinating subject at the crossroad between analysis and geometry. The great quality of this book may be found in the many open-ended directions of research that it suggests and explores."--Bulletin of the London Mathematical Society