The present Teubner-Text contains invited surveys and shorter communications con nected with the International Conference "Function Spaces, Differential Operators and Non linear Analysis," which took place in Friedrichroda (Thuringia, Germany) from September 20-26, 1992. The main subjects are weil reflected by the table of contents. 55 mathematicians attended the conference, many of them from eastern countries. We take the opportunity to thank DFG for financial support, which enabled us to invite mathematicians from the former socialist countries, and especially from the former Soviet Union, and which gave us the pos sibility to maintain and to strengthen our contacts to these centers of the theory of function spaces and its application to PDE's, \li'DE's and approximation theory. The organization of the conference as weil as the final preparation of this text was mostly done by our co-workers in Jena. We wish to thank all of them for the generaus support they gave us far beyond their duties (whatever this means in connection with the organization of a conference). The final preparation of this text was mainly done by Dr. M. Malarski. Fur thermore Dr. M. Geisler, Ms. D. Haroske and Dr. W. Sicke! converted some manuscript in readable papers on TEX-standard Ievel. We wish to thank them for doing this time-consuming work. Jena, May 13, 1993 H.-J. Schmeisser H. Triebe! Contents Survey Articles 9 I Herbert Amann Nonhomogeneaus Linear and Quasilinear Elliptic and Parabolic Boundary Value Pr- lems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Gerard Bourdaud The Functional Calculus in Sobolev Spaces . . . . . . . . . . . . . . . . . . . 127 . . . . ."