Canadian administrative law was bedeviled for many decades by uncertainty and confusion. In 2019, the Supreme Court of Canada sought to bring this chaos to an end in its landmark decision . In , Paul Daly explains why Canada’s administrative law was uncertain and confusing and assesses the proposition that Vavilov provides a roadmap to a brighter future. Looking at administrative law from its historic origins in sixteenth- and seventeenth-century England, identifying the complexity of its underlying structure, and describing divergent judicial attitudes to the growing administrative state, Daly builds a framework for understanding why multiple previous reform efforts failed and why Vavilov might very well succeed. This engaging study shows readers how a newly emerged “culture of justification” allows courts and citizens to insist on the reasoned exercise of public power by the administrative state.