Gallicanism is the belief that popular civil authority—often represented by the monarch's or the state's authority—over the Catholic Church is comparable to that of the Pope. Gallicanism is a rejection of ultramontanism; it has something in common with Anglicanism, but is nuanced, in that it plays down the authority of the Pope in church without denying that there are some authoritative elements to the office associated with being primus inter pares ("first among equals"). Other terms for the same or similar doctrines include Erastianism, Febronianism, and Josephinism.

Gallicanism originated in France (the term derives from Gallia, the Latin name of Gaul), and is unrelated to the first-millennium Catholic Gallican Rite. In the 18th century it spread to the Low Countries, especially the Netherlands. The University of Notre Dame professor John McGreevy defines it as "the notion that national customs might trump Roman (Catholic Church) regulations."