Gaudium et Spes (Ecclesiastical Latin: [ˈɡawdium et ˈspɛs], Joy and Hope), the Pastoral Constitution on the Church in the Modern World, was one of the four Apostolic Constitutions resulting from the Second Vatican Council. The document is an overview of the Catholic Church's teachings about humanity's relationship to society, especially in reference to economics, poverty, social justice, culture, science, technology and ecumenism.

Approved by a vote of 2,307 to 75 of the bishops assembled at the council, it was promulgated by Pope Paul VI on 7 December 1965, the day the council ended. As is customary with Catholic documents, the title is taken from its incipit in Latin:

The document was not drafted before the council met, but arose from the floor of the council and was one of the last to be promulgated. Pope John XXIII, who was deathly ill at the time, was forced to watch the proceedings on closed circuit television. He was too sick to attend, and died within months.

The previous Vatican Council in 1869-70 had tried to defend the role of the church in an increasingly secular world. Those who interpret the purpose of the Second Council as one of embracing this world use Gaudium et Spes as the primary hermeneutic for all its documents. One of the cardinals, Leo Joseph Suenens of Belgium, urged the council to take on social responsibility for Third World suffering, International peace and war, and the poor.