The theme of this research is a historical-systematic reflection on the understanding of the category actuosa participatio in light of the liturgical theology of Joseph Ratzinger/Pope Benedict XVI. This study is part of the research activities of the Graduate Program in Theology at PUC-Rio, within the concentration area of Systematic-Pastoral Theology, in the research line Faith and Culture, linked to the project The Theology of Joseph Ratzinger and the Magisterium of Benedict XVI. The main objective is to investigate how this theme emerges in the theological thought of Joseph Ratzinger and in the magisterium of Pope Benedict XVI, aiming to verify whether his liturgical theology aligns with the understanding of the theme within the framework of conciliar theology. To achieve this objective, the study begins with a reflection that seeks to trace the historical development of the category actuosa participatio throughout the history of Christianity. It then develops through two successive approaches: (1) the presentation and analysis of Ratzinger s liturgical texts in which the theme of actuosa participatio is addressed; and (2) the analysis of this theme within the magisterium of Pope Benedict XVI. These approaches enable an investigation into how Joseph Ratzinger/Pope Benedict XVI understood and developed the concept throughout his theological and magisterial journey, with the aim of corroborating the hypothesis that the conception of actuosa participatio present in his thought is in profound harmony with the understanding of this category within the liturgical theology of the Second Vatican Council. The scope of this research is to contribute to a better dissemination and understanding of the liturgical theology of Joseph Ratzinger/Benedict XVI.