Pope Leo X issued the papal bull Decet Romanum Pontificem, excommunicating Martin Luther for refusing to retract 41 alleged errors found in his 95 Theses and other writings.

Pope Leo X was head of the Catholic Church and ruler of the Papal States from 9 March 1513 to his death in December 1521.

A papal bull is a type of public decree, letters patent, or charter issued by the pope of the Catholic Church. It is named after the leaden seal (bulla) traditionally appended to authenticate it.

Decet Romanum Pontificem is a papal bull issued on 3 January 1521 by Pope Leo X to effect the excommunication of German theologian Martin Luther and some of his colleagues—notably Andreas Karlstadt—for refusing to recant forty-one of Luther's Ninety-five Theses, threatened by the earlier papal bull Exsurge Domine. Luther had burned his copy of Exsurge Domine on 10 December 1520 at the Elster Gate in Wittenberg to indicate his response. The title Decet Romanum Pontificem comes from the first three Latin words of its text.

Martin Luther was a German priest, theologian, author, hymnwriter, professor, and former Augustinian friar. Luther was the seminal figure of the Protestant Reformation, and his theological beliefs form the basis of Lutheranism. He is widely regarded as one of the most influential figures in Western and Christian history.

The Ninety-five Theses or Disputation on the Power and Efficacy of Indulgences is a list of propositions for an academic disputation written in 1517 by Martin Luther, then a professor of moral theology at the University of Wittenberg, Germany. The Theses are retrospectively considered to have launched the Protestant Reformation and the birth of Protestantism, despite various proto-Protestant groups having existed previously. It detailed Luther's opposition to what he saw as the Roman Catholic Church's abuse and corruption by Catholic clergy, who were selling plenary indulgences, which were certificates supposed to reduce the temporal punishment in purgatory for sins committed by the purchasers or their loved ones.