The idea of social investment has obvious intuitive appeal. But is it robust? Is it built on sound philosophical principles and secure analytical foundations? Will it deliver better outcomes? For almost a decade, the idea of social investment has been a major focus of New Zealand policy-making and policy debate. The broad aim has been to address serious social problems and improve long-term fiscal outcomes by drawing on big data and deploying various analytical techniques to enable more evidence-informed policy interventions. But recent approaches to social investment have been controversial. In late 2017, the new Labour-New Zealand First government announced a review of the previous government's policies. As ideas about social investment evolve, this book brings together leading academics, commentators and policy analysts from the public and private sectors to answer three big questions: How should social investment be defined and conceptualized? How should it be put into practice? In what policy domains can it be most productively applied? As governments in New Zealand and abroad continue to explore how best to tackle major social problems, this book is essential for people seeking to understand social policy in the twenty-first century.