"Brownian Motion, Obstacles and Random Media" is a technical book that focuses on developments and techniques in the field of Brownian motion and random obstacles. It provides a comprehensive overview of the ideas and results that have emerged in this research area over the past ten years. The book aims to consolidate the vast amount of information scattered across various sources and make it accessible to non-specialists. The study of Brownian motion is not only mathematically fascinating but is also shaped by the physical heuristics associated with it. A central concept addressed in this context is the "pockets of low local eigenvalues," which play a significant role in the analysis of Brownian motion and random obstacles. These concepts also have connections to other areas of random media and are discussed in detail in the book.