This chapter argues that the roots of Vatican II must be pushed back into the eighteenth century in order to fully understand the council. It profiles the existence and achievements of the “Catholic Enlightenment,” a now well-established phenomenon that spanned the entire European Catholic world, and argues that it was an attempt at aggiornamento. A variety of eighteenth-century movements, many of them later condemned or marginalized by the Church’s official magisterium, are then profiled, including Gallicanism, Richerism, Febronianism, and Josephinism. The chapter then examines a complex and misunderstood reform movement, Jansenism, which especially shaped Scipione de’ Ricci and the Pistoian circle. Finally, it examines a loose “Third Party” of moderate Catholic reformers (who were neither Jansenists nor traditionalist zelanti), focusing on Lodovico Muratori. The chapter shows that both radical Jansenists and moderate “Third Party” Catholics attempted ressourcement, especially in advocating liturgical and devotional reform and encouraging Bible reading.