This book gives a pedagogical introduction to the physics of amorphous solids and related disordered condensed matter systems. Important concepts from statistical mechanics such as percolation, random walks, fractals and spin glasses are explained. Using these concepts, the common aspects of these systems are emphasized, and the current understanding of the glass transition and the structure of glasses are concisely reviewed. This second edition includes new material on emerging topics in the field of disordered systems such as gels, driven systems, dynamical heterogeneities, growing length scales etc. as well as an update of the literature in this rapidly developing field.