Octogesima adveniens 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.
It discusses themes such as securing democratic foundations in society.
The letter is one of the first magisterial documents to mention the topic of the preservation of environment, an issue that was fairly new in the political sphere at the time of the text's publication.