Book excerpt: For several decades, scholars have developed methods for solving optimization problems which emerge in economics, econometrics, operations research, and other disciplines. A considerable effort has been made to construct equations from which constraints can be derived, but surprisingly little has been done to construct the other part of optimization models: the scalar-valued objective function, the constrained maximum or minimum of which gives the optimal solution. The given volume is intended to attract attention to the problem, to present the major achievements in the field and to stimulate further research and teaching.