The Second Vatican Council presents the restoration of Christian unity as a primary concern because division contradicts Christ’s will and obstructs the Gospel. It grounds unity in the Trinity, Christ’s prayer, Baptism, the Eucharist, and the Holy Spirit, while recognising an imperfect but real communion with baptised Christians outside the Catholic Church and the presence among them of Scripture, grace, and other elements of sanctification. Catholics are urged to pursue ecumenism through conversion, prayer, renewal within the Church, respectful theological dialogue, sound ecumenical formation, and cooperation for peace, human dignity, and the relief of poverty. Dialogue must combine clarity about Catholic doctrine with charity and humility, avoiding both polemics and false irenicism while attending to a hierarchy of truths. The Council gives particular attention to the apostolic heritage, valid sacraments, liturgical riches, and legitimate self-governance of the Eastern Churches, and encourages respect for the distinct traditions of Western Christian communities. Full unity remains the goal, but it depends ultimately on Christ’s prayer and the action of the Holy Spirit.