Debates concerning the relationship between Tridentine Catholicism and Catholicism after Vatican II dominate theological conversation today, particularly with regard to the Church and its engagement with the world. Current historical narratives paint ecclesiology after the Council of Trent as dominated by juridical concerns, uniformity, and institutionalism. Purportedly neglected are the spiritual, diverse, and missional aspects of the Church. This book challenges such narratives by investigating the theology of ecclesial unity and catholicity of the renowned Spanish Jesuit Francisco Su?rez (1548-1617). Analyzing standard as well as overlooked sources of Su?rez's ecclesiology, Eric J. DeMeuse shows how Su?rez wrestles with the new demands of his time and anticipates later ecumenical developments in twentieth-century Catholic ecclesiology. Early modern expansion prompted theologians after Trent to reckon with the ecclesial status of baptized Protestants, the Greek Orthodox, and non-believers in the New World. It further prompted reflection on the universality, or catholicity, of the Church, and how the Church's mission to the nations serves her greater unity in Christ. DeMeuse demonstrates Su?rez's vision of the Church to be deeply spiritual, diverse, and missional—not at the expense of the institutional, but as its necessary and life-giving source. This book further explores not only Su?rez's speculative ecclesiology, but how the unity and catholicity of the body of Christ are lived out in practice: in the worship and works of the faithful, and, most notably, in the charism of his own religious order, the Society of Jesus. Su?rez's theology shows what the spiritual dynamic between Christic unity and missional catholicity should look like in the Church.