In this chapter, we focus on bullying prevention, which is a perfect case to discuss the development and evaluation of interventions embedded in an investment-intervention approach. Bullying is a widespread problem across countries, regardless of their level of economic development. It has been associated with short- and long-term deterioration in children's life opportunities and well-being. First, we introduce bullying as a phenomenon and elaborate on its short- and long-term consequences. Next, we briefly present how bullying can be prevented and addressed by interventions in schools and the potential long-term benefits of such efforts for society. Preventive interventions necessitate initial investment but can also be turned into social investment over time. We use the Finnish KiVa® antibullying program as an example. Finally, we elaborate on how this line of thinking – considering prevention and intervention as long-term investments and strengthening various stock and flow factors – could benefit society at large.