Pope Francis has changed the teachings of the Catholic faith to oppose the death penalty in all circumstances, the Vatican has said.
The Catechism of the Church, which sums up the teachings, had previously stated that the death penalty could be used in some cases.
It now says it is "inadmissible because it is an attack on the inviolability and dignity of the person".
Pope Francis has in the past spoken out against executions.
Last October, he had said the Church's policy on the death penalty was one area where teaching was not static and could change with modern concerns.
The text of the catechism was first set by Pope John Paul II in October 1992.
The teachings had earlier stated that the death penalty was "an appropriate response to the gravity of certain crimes and an acceptable, albeit extreme, means of safeguarding the common good".
However, the new text says there is "an increasing awareness that the dignity of the person is not lost even after the commission of very serious crimes".
It also argues that today's more effective detention methods protect citizens and "do not definitively deprive the guilty of the possibility of redemption".
The Church will now work with determination for the abolition of the death penalty worldwide, a statement from the Holy See said.
Historically, the Church has mostly been unopposed to the death penalty, including into the 20th Century. In 1952, Pope Pius XII said it was not a violation of the universal right to life.
Pope John Paul II argued for imprisonment over execution wherever possible, although Joseph Ratzinger, who later became Pope Benedict XVI, wrote that the death penalty could be permissible.
