Journal article: We illustrate how randomised controlled trials (RCTs) could be used to evaluate the impact of alternative designs of the common agricultural policy (CAP). We select four policy-design issues which relate to different components of the CAP and raise a wide range of economic questions: nudges, coordination failures, equity-efficiency trade-offs, contract design. Based on examples from agricultural and social policies in developing and developed countries, we show that RCTs have provided useful rigorous evidence on similar design issues, suggesting that they could also be leveraged to help improve components of the CAP.