There are many points of contact between optimization problems and modeling. On the one hand the model adjustment process itself as a process of estimation is closely connected with optimization, in that it is to produce what is in one sense the best possible model. The basic structure of the optimization problem as problem in decision making with the necessary input of a n objective function is thus evident. On the other hand a model is never a n end in itself but on the basis of its simulation capacity a means to an end, for example in biotechnological optimization. From this point of view the model is 8 product of scientific work and thus a n economic value. Equally, through its intended purpose the model exhibits a utility value. A complete evaluation of the model R R a condition of rational modeling must take into account both these aspects. That is possible in principle by adding the modeling expenditure to expenditure for the realization of biotechnological processes, expressing the economic consequences of model quality ns an objective function, and minimizing the specific total expenditure for the product to be produced. Biotechnological practice requires that the "optimum" model is approached by means of iterative processes. Some practical examples nil1 make the process clear, taking into acconnt qualitative (semantic) and quantitative (accuracy) aspects of the utility value.