Tjalling Koopmans has made fundamental contributions to three major areas of modern quantitative economics. The first is the statistical identification and estimation of parameters in econometric models. The second is activity analysis, of which what is popularly known as linear programming is one aspect. The third is intertemporal utility maximization and the optimum allocation of resources over time. Most economists would be pleased to make seminal contributions in just one area as he has done in each. In making our selection of his papers to be included in this volume, we have attempted to include significant contributions in each of the major areas of Koopmans’ work.

We have tried as well to give some idea of the extraordinary breadth of the man and his work. It is for this reason that we have included one of his two published papers in physics, “Über die Zuordnung von Wellenfunktionen und Eigenwerten zu den einzelnen Elektronen eines Atoms,” a paper which is still referred to in basic physics texts. Although we were greatly tempted to include a major portion of Koopmans’ Ph.D. dissertation in mathematical statistics at the University of Leiden, we found that the entire dissertation was far too long and that a meaningful sub-section was difficult to extract because of the relative unfamiliarity of the basic approach to modern readers. Again both length and difficulty of condensation precluded inclusion of material from Tanker Freight Rates and Tankship Building, a careful empirical investigation into a problem of considerable contemporary significance.