Police enforce the law, but they must also obey it. Statutes circumscribe how law enforcement officers conduct their work. At the same time, Canadian 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 rescind powers when the police tactics they enable become controversial? This nuanced book surveys the evolution, application, and future of judge-made police powers. The authors bring historical perspective, critical legal theory, and empirical analysis to an issue that is fundamental to constitutional protection from state interference with individual liberty.