Most of the solid materials we use in everyday life, from plastics to cosmetic gels exist in a non-crystalline, amorphous form: they are glasses. Yet, we are still seeking a fundamental explanation as to what glasses really are, why they form, and what their properties are. This book surveys the most recent theoretical and experimental research dealing with the physics of glassy and disordered materials, from molecular fluids to colloidal glasses, granular media and foams. Chapters present broad and original perspectives on one of the deepest mystery of condensed matter physics, with a particular emphasis on the key role played by dynamic heterogeneities to understand from a unified viewpoint phenomena occurring in scores of disordered materials. The book covers both fundamental aspects, and reviews extensively several recent theoretical developments in the field of the glass transition that have changed our view of the glass transition. It also provides an up-to-date perspective on new experimental tools that have been developed to study with unprecedented resolution the structural relaxation of systems like molecular and polymer liquids, colloidal glasses, foams and granular materials. It also confronts, discusses, compares, and challenges the different perspectives actively promoted by different research groups and communities in a very active area of condensed-matter and statistical physics.