This study examines the effects of counterterrorism policing tactics on public cooperation among Muslim communities in London, U.K. The study reports results of a random-sample survey of 300 closed and fixed response telephone interviews conducted in Greater London's Muslim community in February and March 2010. It tests predictors of cooperation with police acting against terrorism. Specifically, the study provides a quantitative analysis of how perceptions of police efficacy, greater terrorism threat, and the perceived fairness of policing tactics (“procedural justice”) predict the willingness to cooperate voluntarily in law enforcement efforts against terrorism. Cooperation is defined to have two elements: a willingness to work with the police in anti-terror efforts, and the willingness to alert police upon becoming aware of a terror-related risk in a community. We find that among British Muslims, both measures of cooperation are better predicted by procedural justice concerns than by perceptions of police efficacy or judgments about the severity of the terrorism threat. Unlike previous studies of policing in the United States, however, we find no correlation between cooperation and judgments about the legitimacy of police; rather, procedural justice judgments influence cooperation directly.