The main features of this volume are: 1) It is devoted to the basic principles of asymptotics and their applications; 2) It presents both traditional approaches as well as less widely used and new approaches such as one- and two-point Pade Approximants, constitutive equations, methods of boundary perturbations, etc.; 3) A general introduction to the subject suitable for non-specialists. Compared with other published books in the field the authors have paid special attention to examples and the discussion of results rather than burying them in formalism, in notation and in technical details. Audience: Researchers in mechanics, physics and applied mathematics as well as in engineering. Graduate students and even high school students can benefit from reading the book, which does not require any scientific knowledge of mathematics and physics.