This work explores the history of the Catholic Church in France from 1900 to 1950, a period marked by profound transformations in the political, social, and cultural fabric of the nation. The Church's role during this tumultuous half-century was defined by its response to key historical events, including the separation of Church and State in 1905, the socio-political upheavals of the two world wars, the challenges posed by secularism, and the moral reckoning brought about by the Vichy regime and the Holocaust. The study examines how the Church navigated ideological conflicts over national identity, education, and social justice, revealing a complex interplay between tradition and reform, collaboration and resistance, and theological orthodoxy and intellectual innovation. Central to this period were movements such as Catholic Action, the Jeunesse Ouvrière Chrétienne (JOC), and the Worker-Priest Movement, which sought to bridge the gap between the Church and the working class. Prominent Catholic intellectuals, including Jacques Maritain, Emmanuel Mounier, and Henri de Lubac, developed philosophical frameworks that addressed the ethical dilemmas of modernity and articulated visions of Christian democracy, personalism, and spiritual renewal. The work also investigates the Church's response to anti-Semitism and its role in the Resistance, highlighting both heroic acts of moral courage and moments of silence and complicity. The immediate post-war period witnessed a renewed commitment to social engagement, with initiatives such as Secours Catholique symbolizing the Church's dedication to humanitarian aid and rebuilding efforts. However, internal tensions persisted regarding the Church's relationship with the secular Republic, the nature of clerical identity, and the boundaries of political activism. Through an analysis of primary sources, papal encyclicals, theological writings, and the contributions of Catholic cultural figures, this study underscores the multifaceted nature of French Catholicism during this era. The Church's struggles and achievements during these fifty years laid the groundwork for the reforms of the Second Vatican Council and its renewed engagement with the modern world. Ultimately, the history of the Catholic Church in France from 1900 to 1950 illustrates the enduring challenge of living out the Gospel in the face of profound social and moral upheaval, as well as the Church's capacity for resilience, reflection, and renewal.