This work presents an analysis of the presidency of Plutarco Elías Calles. It views Calles as a man of the Mexican Revolution and as an heir to the values promoted by the Constitution that came as a result of this movement. His respect for the constitution, pushed him to act on his anticlerical beliefs and to unify the Revolutionary movement under one party. Focusing mostly on the reasons and results of his anticlerical policy, we hope to gain insight into Calles’ constitutionalism. By understanding Calles’ policies, we can understand both the nature of the peculiar separation of Church and State in a very religious country, and the reasons for the formation of a party that would rule Mexico for seventy-two years.