Ascertaining the optimum global population raises not just substantive moral problems but also philosophical ones, too. In particular, serious problems arise for utilitarianism. For example, should one attempt to bring about the greatest total happiness or the highest level of average happiness? This article argues that neither approach on its own provides a satisfactory answer, and nor do rights-based or Rawlsian approaches, either. Instead, what is required is a multidimensional approach to moral questions—one which recognises the plurality of our values. (...) Such an approach can be formalised by employing multidimensional indifference-curves. Moreover, whereas classical utilitarianism might be thought to enjoin us to bring about a larger global population, a multidimensional approach clearly suggests a significant reduction in human numbers. (shrink)