A growing body of research has shown that people's motivations to cooperate with the police and not break the law are shaped more by feeling the police have legitimate authority, and share the same values, than by people's perceived risk of being caught and punished. Given public perceptions of fair treatment are at the root of police legitimacy, improved policepublic interactions over the long term could help reduce crime. There is limited evidence on which interventions can improve public perceptions of fair treatment by the police. The Randomised Controlled Trial (RCT) reported in this paper tested the impact of training on the perceived quality of interactions between the police and crime victims in Greater Manchester. The intervention focused on developing officers' practical communication skills. In total, 339 officers were randomly assigned to the treatment group (to receive the training) and 237 to the control group (to not receive the training). As the officers were assigned at random, differences between the groups after the training can be directly attributed to the intervention. RCTs are considered the 'gold standard' in evaluation research as they can establish 'cause and effect' relationships.