The principal purpose of this book is to provide an account of the
circle of ideas, results and techniques, which emerged roughly over the
last ten years in the study of Brownian motion and random obstacles. The
accumulation of results in many separate sources eventually made it
impractical, if not impossible, for the nonspecialist to gain access to
the developments of the subject. This book is an attempt to remedy this
situation. Part of the thrill of the investigation of Brownian motion
and random obsta- cles certainly stems from its many connections with
various areas of math- ematics, but also from the formal and mysterious
physical heuristics which relate to it. In particular the loose concept
of pockets of low local eigenval- ues plays an important role in the
study of Brownian motion and random obstacles, and also represents a
paradigm which has natural resonances with several other areas of random
media. This last feature has increasingly be- come clear over the last
few years.