Social investment has become a widely debated topic in the comparative welfare state literature. To date, there are, however, only a couple of systematic comparative empirical analyses that focus on the employment outcomes associated with social investment. This study contributes to the social investment literature by empirically analysing the extent to which variation in employment outcomes across 26 OECD countries over the period 1990-2010 can be explained by effort on five social investment policies using time-series cross-sectional analyses. Apart from focusing on employment rates, we additionally explore associations with qualitative aspects of the employment outcomes relying on novel indicators. The analyses account for theoretically relevant confounding variables that were omitted in existing studies, notably labour market institutions. We find robust evidence for a positive association between effort on active labour market policies and employment rates. For other policies we obtain mixed results, dependent on the employment outcome being studied. Subsequently, we explore the role of policy and institutional complementarities in the assessment of the employment effects of social investment policies. We show how social investment policies interact and how their effect is moderated by effort on other policies. Additionally, our analysis shows that the complementarity of social investment policies varies across welfare state regimes. Finally, explorative analyses suggest that there are positive synergies between more and better jobs, which could in part be attributable to effort on social investment.