This book is an extensive study of the theory of homogenization of partial differential equations. This theory has become increasingly important in the last two decades and it forms the basis for numerous branches of physics like the mechanics of composite and perforated materials, filtration and disperse media. The book contains new methods to study homogenization problems, which arise in mathematics, science and engineering. It provides the basis for new research devoted to these problems and it is the first comprehensive monograph in this field. It will become an indispensable reference for graduate students in mathematics, physics and engineering.