In Protestant Reformation history, confessionalization is the parallel processes of "confession-building" taking place in Europe between the Peace of Augsburg (1555) and the Thirty Years' War (1618–1648).
For most of this time, there was a nominal peace in the Holy Roman Empire between the Protestant and Catholic confessions as both competed to establish their faith more firmly with the population of their respective areas.
Calvin's Geneva is also a model case for the confessional era because of its high degree of social control, unity and homogeneity under one expression of a reformed Christian faith.
Confessionalization was supported by monarchs and rulers in general, because after the Reformation had brought control over their territories' churches into their hands, they could exercise more power over their subjects by enforcing strict religious obedience.
Nancy Shields Kollmann used the term "confessionalization" to refer to the religious arbitration and control used in the Russian Empire to manage the activity of non-Orthodox religions such as Catholicism, Lutheranism, Islam, Judaism, and Buddhism.