This article examines the development of the doctrine of the ‘permanent constituent power’ in Mexico. This doctrine reflects a long tradition in constitutional theory according to which the exercise of constituent power is a one-time event: once a constitution is adopted, there will be no legal mechanism in place for the exercise of the people’s original constitution-making authority. This view is nonetheless in tension with a notion that has also been historically embraced by liberal constitutionalism: that the people has an inalienable right to alter the form of government. The constitutional provisions that reflect that idea, we will see, can have important implications in terms of the nature and scope of the amending authority and, at the same time, point toward alternative mechanisms for the exercise of constituent authority. By closely examining the operation of those kinds of provisions in the Mexican constitution, we seek to illustrate a tension central to the liberal constitutional tradition and to suggest a way out of it. In so doing, we aim to draw some lessons from the Mexican case that can contribute to current discussions about constituent power and fundamental constitutional change in liberal constitutional orders.