This volume presents the collection of mathematical articles by Martin Kneser, reprinted in the original language - mostly German -, including one yet unpublished. Moreover, also included is an article by Raman Parimala, discussing Kneser's work concerning algebraic groups and the Hasse principle, which has been written especially for this volume, as well as an article by Rudolf Scharlau about Kneser's work on quadratic forms, published elsewhere before. Another commentary article, written by Günter M. Ziegler especially for this volume, describes the astounding influence on the field of combinatorics of what was published as "Aufgabe 360" and its subsequent solution in 1955 resp. 1957 in the "Jahresbericht der Deutschen Mathematiker-Vereinigung". However, as the titles of the articles show, Kneser's mathematical interests were much broader, which is beautifully discussed in an obituary by Ulrich Stuhler, included as well in this volume.