'Peace on Earth') is a papal encyclical issued by Pope John XXIII on 11 April 1963, on the rights and obligations of people and their states, as well as proper interstate relations.

The short title Pacem in terris is derived from the opening words of the encyclical, as is customary with papal documents: Pacem in terris was the first encyclical that a pope addressed to "all men of good will", rather than only to Catholics, quoting the praise to God as said by the heavenly army above the manger of Bethlehem (Latin Vulgate: in terra pax in hominibus bonae voluntatis, Luke 2:14; English translation: 2:13–14).

"[4] In theological terms, it marked a major shift in papal teaching from reliance on classical scholastic categories of natural law to a more inductive approach based on the signs of the times.

Coming just months after the 1962 Cuban Missile Crisis, during which the Vatican served as an intermediary between the White House and the Kremlin,[6] the document also reflected the Pope's experience of 1960 in trying to resolve difficulties arising out of the four-power occupation of Berlin.

[9] In Pavan's view Pacem in terris would present the teachings of Leo XIII on the eternal law, "in light of the changing tides of history, and allow them to resonate with a much wider audience".

"[4] F. Russell Hittinger describes the encyclical "as a kind of magna carta of the Catholic Church's position on human rights and natural law".

[11][12] During an event held on 6 May 2019, in Bulgaria, where John XXIII had gained a reputation for protecting Jews when serving as the country's Vatican representative,[13] Pope Francis invoked the encyclical as a "code of conduct" for peace between Catholics and other religions.