When the Supreme Court of Canada makes a decision that invalidates a statute, it creates a constitutional moment. But does that have a direct and observable impact on public policy? Constraining the Court explores what happens when a statute involving a significant public policy issue – French language rights in Quebec, supervised consumption sites, abortion, or medical assistance in dying – is declared unconstitutional. James B. Kelly examines the conditions under which Parliament or provincial/territorial legislatures attempt to contain the policy impact of judicial invalidation and engage in non-compliance without invoking the notwithstanding clause. He considers the importance of the issue, the unpopularity of a judicial decision, the limited reach of a negative rights instrument such as the Charter, the context of federalism, and the mixture of public and private action behind any legislative response. While the Supreme Court’s importance cannot be denied, this rigorous analysis convincingly concludes that a judicial decision does not necessarily determine a policy outcome.