Octogesima adveniens (The eightieth anniversary) is the incipit of the 14 May 1971 Apostolic Letter addressed by Pope Paul VI to Cardinal Maurice Roy, president of the Pontifical Council for the Laity and of the Pontifical Council for Justice and Peace, on the occasion of the eightieth anniversary of Pope Leo XIII's encyclical Rerum novarum.

Generally known as A Call to Action on the Eightieth Anniversary of Rerum novarum, it is an Apostolic Letter which discusses themes such as securing democratic foundations in society.

[1]Sections 8 through 21 address particular social concerns, most especially the effect of increased urbanization: "Is sufficient attention being devoted to the arrangement and improvement of the life of the country people, whose inferior and at times miserable economic situation provokes the flight to the unhappy crowded conditions of the city outskirts, where neither employment nor housing awaits them?

It is not enough to recall principles, state intentions, point to crying injustice and utter prophetic denunciations; these words will lack real weight unless they are accompanied for each individual by a livelier awareness of personal responsibility and by effective action.

Unlike Leo XIII’s encyclical Rerum novarum, Paul VI extends this postulate also on the natural environment and stresses the responsibility for future generations (no.