This introduction to our special issue on ‘Constitutional Legitimacy and Amendments’ presents a framework for a more nuanced understanding of how constitutional change is contested, moving beyond the conventional notion of ‘unconstitutional’ constitutional amendments. We advocate for a clearer distinction between legality and legitimacy when analysing contestation over constitutional change, arguing that focusing exclusively on legality without addressing legitimacy risks oversimplifying constitutional debates and overlooking questions of broader political and social acceptance. We identify three grounds on which the legitimacy of a constitutional amendment may be challenged: lack of representativeness (an amendment is illegitimate if it is not representative of the will of the people); lack of justice (an amendment is illegitimate if it is unjust in a significant manner); and bad faith (an amendment is illegitimate if it is motivated by ulterior motives). We also outline three ways in which legality and legitimacy intersect: (1) legally valid amendments may still face challenges regarding their legitimacy; (2) formally illegal constitutional changes may still be perceived as legitimate; and (3) even amendments that are both legal and legitimate may still require legitimacy to be established through means other than procedural and substantive commitments to legality. By recognising that challenges to constitutional amendments often involve claims of both legality and legitimacy, our framework expands the analysis of constitutional amendments beyond claims based on constitutional identity or unamendability and contributes to a better understanding of how such amendments are contested.