The U.S. Government is committed to learning what works to reduce poverty and increase food security through agriculture investments. There are many tools for learning from program experience. However, impact evaluations are central to a learning agenda that moves beyond business-as-usual assumptions about what works. There is no more rigorous tool than impact evaluation to answer difficult questions such as: Did we achieve the impact we intended? Did we make the right assumptions about how project interventions would translate into poverty reduction? What is the impact of our investment as compared to what would have happened without it? What impacts are directly attributable to this investment, and not to other factors? In other words, what can the investment really take credit for? Did the benefits of this investment outweigh the costs? What can we learn from what went right and what went wrong? When impact evaluations are rigorous and independent, and coupled with a commitment to transparency, they are a powerful tool for accountability, learning and making investments based on evidence about what works.