Police enforce the law, but they must also obey it. Statutes circumscribe how law enforcement officers conduct their work. Controls on police power are also embedded in the decisions written by judges, spawning a controversial area of legal debate — and of policing itself. The courts have handed police many powers to stop, search, and otherwise investigate people in the pursuit of public safety and crime prevention. Ancillary Police Powers in Canada explains what these common-law police powers are; how they came to be; and, crucially, what the potential dangers are in their expanding scope. What is the difference between police duty and lawful authority? Should the Supreme Court revisit and possibly rescind powers when the police tactics they enable become controversial? This nuanced book surveys the evolution, application, and future development of judge-made police powers in Canada from various points of view. The authors, with backgrounds in law, policing, and criminal justice, bring historical perspective, critical legal theory, and empirical analysis to bear on an issue that is fundamental to constitutional protection from state interference with individual liberty. The result is a unique and thought-provoking journey into the changing practice of Canadian policing.