The book offers a critical reflection on the right interpretation of the terminology of renewal (renovatio), reform (reformatio) and other related expressions such as purification, innovation, restoration, accommodation, correction, and aggiornamento in the sense of adaptation. By engaging both the protagonists and critics of the conciliar renewal and reform, the book pays attention to the tension that exists between continuity and discontinuity, reform and discontinuity, as well as, between fidelity and dynamism in handing on the deposit of faith (depositum fidei). Focusing on Lumen Gentium and Unitatis Redintegratio, it demonstrates the extent to which the idea of renewal and reform has been received in the post-conciliar ecclesiology. Such articulation is equally relevant for interpreting the ongoing renewal and reform of the Catholic Church itself.