The concept of the social investment welfare state has received a lot of attention and support both from academics and policymakers. It is therefore commonly assumed that policies such as investing in education or family services would also receive significant support from the mass public. While there are some indications of this, existing comparative e surveys of public opinion usually do not take into account how citizens perceive and react to policy trade-offs, i.e. how they respond when force d to prioritize between different types of social policies, which is more realistic given budget constraints. This article presents original data from a representative survey of public opinion in eight Western European countries, studying how support for social investment policies changes when additional spending on these policies would have to be financed with cutbacks in other parts of the welfare state. The central findings are that citizens generally dislike being forced to cut back one type of social spending to expand another, but there is a significant degree of variation across individuals and policy fields. Material self-interest and ideological predispositions as well as their interaction help understanding differences in the acceptance of these trade-offs. The findings have important implications for the political viability of social investment policies. Political parties aiming to expand social investment in a context of fiscal austerity are confronted with different and distinct electoral constraints and challenges given the respective preferences of their electorates.