Thepresentbookisamemorialvolumedevotedtoourfriend,colleagueandteacher Peter Jonas who passed away on July 18, 2007. It displays recent advances in modern operator theory in Hilbert and Krein spaces and contains a collection of original research papers written by participants of the 7th Workshop on Operator Theory in Krein Spaces and Spectral Analysis, which was held at the Technische Universit. at Berlin, Germany, December 13 to 16, 2007. The articles in this v- ume contain new results for problems close to the area of research of Peter Jonas: Spectralandperturbationproblemsfor operatorsininner productspaces,gener- ized Nevanlinna functions and de?nitizable functions, scattering theory, extension theory for symmetric operators, ?xed points, hyperbolic matrix polynomials, - ment problems, inde?nite spectral and Sturm-Liouville problems, and invariant subspace problems. It is a pleasure to acknowledge the substantial ?nancial support for the 7th Workshop on Operator Theory in Krein Spaces and Spectral Analysis received from the - Berlin Mathematical School (BMS) - Gesellschaft fur .. Angewandte Mathematik und Mechanik (GAMM) - International Mathematical Union, Commission on Development and Exchanges - Institute of Mathematics of the Technische Universit. at Berlin The Editors Peter Jonas (1941-2007) In Memoriam Peter Jonas (1941-2007) Jussi Behrndt, Karl-Heinz F.. orster and Carsten Trunk Peter Jonas was born on July 18, 1941, in Memel, now Klaipeda, which was at thattime the mosteasterntownofEastPrussia.After the war,PeterJonasmoved with his mother and grandmother to Blankenfelde - a small village near Berlin, where he lived until the end of his school education.