Many Portuguese holidays, festivals and traditions have a Christian origin or connotation. Although relations between the Portuguese state and the Roman Catholic Church were generally amiable and stable since the earliest years of the Portuguese nation, their relative power fluctuated. In the 13th and 14th centuries, the church enjoyed both riches and power stemming from its role in the reconquest, its close identification with early Portuguese nationalism and the foundation of the Portuguese educational system, including the first university. The growth of the Portuguese overseas empire made its missionaries important agents of colonization, with important roles in the education and evangelization of people from all the inhabited continents. The growth of liberal and nascent republican movements during the eras leading to the formation of the First Portuguese Republic (1910–26) changed the role and importance of organized religion.

In what religion do many Portuguese holidays and festivals find their origin?