Field experiments with police agencies represent a new frontier in collaboration between researchers and the public sector. This chapter explores the practical and ethical challenges inherent in partnerships with the police, sharing reflections and lessons from our experiences in the six countries included in the study. We describe what we have learned from both scholarship and experience about how to build effective partnerships and to design ethical interventions with the goal of informing the next generation of research–practice partnerships on issues of public order, security, and policing.