Sobolev spaces play an outstanding role in modern analysis, in
particular, in the theory of partial differential equations and its
applications in mathematical physics. They form an indispensable tool in
approximation theory, spectral theory, differential geometry etc. The
theory of these spaces is of interest in itself being a beautiful domain
of mathematics. The present volume includes basics on Sobolev spaces,
approximation and extension theorems, embedding and compactness
theorems, their relations with isoperimetric and isocapacitary
inequalities, capacities with applications to spectral theory of
elliptic differential operators as well as pointwise inequalities for
derivatives. The selection of topics is mainly influenced by the
author's involvement in their study, a considerable part of the text is
a report on his work in the field. Part of this volume first appeared in
German as three booklets of Teubner-Texte zur Mathematik (1979, 1980).
In the Springer volume "Sobolev Spaces", published in English in 1985,
the material was expanded and revised. The present 2nd edition is
enhanced by many recent results and it includes new applications to
linear and nonlinear partial differential equations. New historical
comments, five new chapters and a significantly augmented list of
references aim to create a broader and modern view of the area.