AbstractDemocratic constitutions often entrench provisions against formal amendment. For example, republicanism is formally unamendable in Italy, as is federalism in Germany, political pluralism in Portugal and secularism in Turkey. Neither the Canadian Constitution nor the United States Constitution entrenches a similar form of formal unamendability, but both entrench a peculiar form of unamendability that results not from constitutional design or constitutional law but from constitutional politics. Constructive unamendability derives from a political climate that makes it practically unlikely, though not the oretically impossible, to meet the high thresholds the constitution sets for formal amendment unless constitutional politics somehow perform heroics. Faced with the constructive unamendability of a rule they wish to formally amend, political actors may resort to arguably legal though illegitimate methods to circumvent the strictures preventing formal amendment. This paper classifies the many forms of unamendability, develops the concept of constructive unamendability, illustrates that the Senate in both Canada and the United States is constructively unamendable, and suggests how Canadian and American political actors might illegitimately amend the constructively unamendable Senate, a strategy the Government of Canada intended to pursue before the Supreme Court of Canada repudiated its Senate reform efforts in the recent Senate Reform Reference.