This chapter provides a critical analysis of Mexican constitutionalism. For Pou, this is characterized by “reformism”, i.e., the capacity simultaneously to maintain close ties with the political/legal past and also to present itself as a system in continuous and uninterrupted transformation. The analysis of Mexican reformism advanced by Pou is both static and dynamic and is organised as follows: first, she presents the basic structure of the Mexican constitutional model; second, she provides an analysis of its key content: the standards, institutions, and substantive rules that form its backbone; third, she provides an assessment of the decision-making processes permitted and promoted by the Constitution; fourth and last, she evaluates what she calls the frequency variable, which is nothing other than weighing the effects that living under a constantly-changing constitutional regime has had on Mexicans. Pou concludes that, in a context of institutional fragility and social and political exclusion, the reformism that characterizes the Mexican system has allowed profound institutional change to be perpetually controlled and prevented from above. Pou likewise concludes that the Mexican legal and political system will only be successful if there is a radical qualitative change in its institutions, rules, and principles.