The subject of this book is the new field of squeezing in quantum fields. This general area includes all types of systems in which quantum fluctuations are reduced below those in the normal vacuum state. The book covers the main currently known techniques of generating squeezed photon fields, together with some treatment of matter field squeezing. Both theory and experiments are covered, together with applications to communications and measurement. The chapters of the book are written by the foremost international experts in the field, and their coverage extends from general introductory material, to the most recent developments.