In 1981 I was approached by Klaus Peters to assist in publishing a selection of the papers of Kurt Otto Friedrichs. With some reluctance Friedrichs has agreed to help in making the selection although in the initial stages only one paper [47-2] was in his opinion worthy of being included. With some coaxing on my part the selection was made mainly by Friedrichs despite his frequent modest grumble that it did not make sense to include "that" paper as "X" had subsequently improved either the result or the proof. Later P.D. Lax and L. Nirenberg identified appropriate papers and, perhaps not so remarkably, there was almost complete overlap. The vast majority of the papers are in partial differential equations and spectral theory where Friedrichs had the greatest impact. For these Peter Lax and Tosio Kato have written the commentaries. Friedrichs made fundamental contributions in the theory of asymptotics; two papers, including Friedrichs' Gibbs Lecture, have been reviewed by W. Wasow. The very profound contributions Friedrichs made to applied mathematics are represented by some papers in elasticity, mainly written with J.J. Stoker and now reviewed by F. John and in magneto-hydrodynamics where Friedrichs' original notes have been reproduced and his contributions to the subject reviewed by Harold Weitzner. In both these areas Friedrichs recognized and clarified approximations made in engineering and physics.

- Volume 1.- The Life of Kurt Otto Friedrichs.- The Life of Kurt Otto Friedrichs.- Publications of Kurt Otto Friedrichs - 1927-1982.- Publications of Kurt Otto Friedrichs - 1927-1982.- I Papers in partial differential equations Commentaries by Peter D. Lax.- [27-3] Über die Eindeutigkeit und das Abhängigkeitsgebiet der Losungen beim Anfangswertproblem linearer hyperbolischer Differentialgleichungen, (With H. Lewy).- [28-2] Über die partiellen Differenzengleichungen der mathematischen Physik, (With R. Courant and H. Lewy).- [67-2] On the partial differential equations of mathematical physics (translation of [28-2]).- [44-1] The identity of weak and strong extensions of differential operators.- [47-1] A theorem of Lichtenstein.- [48-2] Nonlinear hyperbolic differential equations for functions of two independent variables.- [53-4] On the differentiability of the solutions of linear elliptic differential equations.- [32-1] Über fortsetzbare Anfangsbedingungen bei hyperbolischen Differentialgleichungen in drei Veränderlichen, (With H. Lewy).- [54-1] Symmetric hyperbolic linear differential equations.- [58-1] Symmetric positive linear differential equations.- [65-1] Boundary value problems for first order operators, (With P.D. Lax).- [67-1] On symmetrizable differential operators, (With P.D. Lax).- [71-1] Systems of conservation equations with a convex extension, (With P.D. Lax).- Acknowledgements.