The Counter-Reformation was the period of Catholic resurgence that was initiated in response to the Protestant Reformation. It began with the Council of Trent (1545–1563) and largely ended with the conclusion of the European wars of religion in 1648. Initiated to address the effects of the Protestant Reformation, the Counter-Reformation was a comprehensive effort composed of apologetic and polemical documents and ecclesiastical configuration as decreed by the Council of Trent. The last of these included the efforts of Imperial Diets of the Holy Roman Empire, heresy trials and the Inquisition, anti-corruption efforts, spiritual movements, and the founding of new religious orders. Such policies had long-lasting effects in European history with exiles of Protestants continuing until the 1781 Patent of Toleration, although smaller expulsions took place in the 19th century.

Such reforms included the foundation of seminaries for the proper training of priests in the spiritual life and the theological traditions of the Church, the reform of religious life by returning orders to their spiritual foundations, and new spiritual movements focusing on the devotional life and a personal relationship with Christ, including the Spanish mystics and the French school of spirituality.

It also involved political activities that included the Spanish Inquisition and the Portuguese Inquisition in Goa and Bombay-Bassein etc. A primary emphasis of the Counter-Reformation was a mission to reach parts of the world that had been colonized as predominantly Catholic and also try to reconvert nations such as Sweden and England that once were Catholic from the time of the Christianisation of Europe, but had been lost to the Reformation.

Key events of the period include: the Council of Trent (1545–63); the excommunication of Elizabeth I (1570), the codification of the uniform Roman Rite Mass (1570), and the Battle of Lepanto (1571), occurring during the pontificate of Pius V; the construction of the Gregorian observatory in Rome, the founding of the Gregorian University, the adoption of the Gregorian calendar, and the Jesuit China mission of Matteo Ricci, all under Pope Gregory XIII (r. 1572–1585); the French Wars of Religion; the Long Turkish War and the execution of Giordano Bruno in 1600, under Pope Clement VIII; the birth of the Lyncean Academy of the Papal States, of which the main figure was Galileo Galilei (later put on trial); the final phases of the Thirty Years' War (1618–48) during the pontificates of Urban VIII and Innocent X; and the formation of the last Holy League by Innocent XI during the Great Turkish War (1683–1699).