Vatican I and Vatican II represent two of the three ecumenical councils in modern times, yet relatively few studies have sought to understand their relation to one another. In fact, the councils are often positioned as mutually exclusive so that one must choose Vatican I’s Vatican II’s presentations of church and ecclesial authority. Failing to understand the relationship between these councils inhibits the church’s self-understanding and risks misinterpreting key aspects of its own tradition; further, it limits the church’s ability to teach effectively on topics of concern to modern women and men, such as authority, freedom, and ecclesiology. uses the questions of , and the councils taught to frame and demonstrate significant points of continuity, complementarity, and difference between them. It argues that only by seeing Vatican I Vatican II as communicating vital dimensions of the Christian faith can the church’s living tradition be fully appreciated and speak meaningfully to modern Christian women and men.