1. The Feynman-Kac Formula and Semigroups.- 2. Some Potential Theory.- 3. Some Principal Eigenvalue Estimates.- 4. The Method of Enlargement of Obstacles.- 5. Lyapunov Exponents.- 6. Quenched Path Measure and Pinning Effect.- 7. Overview, further Results and Problems.- References.

This book provides an account for the non-specialist of the circle of ideas, results and techniques, which grew out in the study of Brownian motion and random obstacles. It also includes an overview of known results and connections with other areas of random media, taking a highly original and personal approach throughout.