In this paper parallel universes are defined by their relation to multi-criteria optimization combined with an explicit or implicit link for the unambiguous identification of an optimum. As an explicit link function the desirability index is introduced. Desirabilities are also used for restricting the Pareto set to desired parts. Keywords. Parallel Universes, Multi-Criteria Optimization, Pareto Optimization, Desirability Index, Desirability Functions 1 Parallel Universes In this paper it is shown how multi-criteria optimization (MCO) fits into the possible notion of parallel universes. We think of one universe as one view of the universe, i.e. as one quality of the universe represented by one response. Analogously we think of parallel universes as many views of the universe, i.e. many qualities or many criteria connected by a link for comparison of outcomes of the individual criteria. This link appears to be an important feature of parallel universes since without it the single univ...