Ordinary foams such as the head of a glass of beer, and more exotic ones such as solid metallic foams, raise many questions for the physicist. A substantial research community bas grown up in recent years to study these substances. This book describes the results of extensive experiments, computer simulations and theories in an authoritative yet informal style, making ample use of illustrations and photographs. As an introduction to the whole field of the physics of foams it puts a strong emphasis on liquids, while also including solid foams. Simple, idealized models are adopted and their consequences explored. Specific topics include: structure, drainage, rheology, conductivity and coarsening. A minimum of mathematics is used, and theory and experiment are described together at every stage. A guide to further reading is provided through carefully selected references. This is a complete and coherent introduction to the subject which no other modern text currently offers.