Peter the Hermit (c. 1050 – 8 July 1115 or 1131), also known as Little Peter, Peter of Amiens (French: Pierre d'Amiens) or Peter of Achères (French: Pierre d'Achères), was a Roman Catholic priest of Amiens and a key figure during the military expedition from France to Jerusalem in 1096 known as the People's Crusade. Amongst Jews he is best remembered for the massacres of Jews that occurred under his leadership and the precedent they set for subsequent Crusades. He has sometimes been called "Blessed" Peter the Hermit, although he has not been beatified in the Catholic Church.

He is called Pierre l'Ermite in French. The structure of this name in French, unlike its English translation, has led some francophone scholars to treat l'Ermite as a surname rather than a title.

According to some authors, Peter was born around 1050, the son of Renauld L'Ermite of Auvergne and his wife Alide Montaigu, de Picardie. Others claim he was a member of the L'Hermite family of Auvergne in the Netherlands. These claims are disputed by still other authors, who argue that no evidence can confirm that "the Hermit" was an actual surname, and that surnames did not develop until after his time.

According to Anna Komnene's Alexiad (1148), Peter attempted a pilgrimage to Jerusalem before 1096, but was prevented by the Seljuk Turks from reaching his goal and was reportedly mistreated. He was said to have witnessed scenes that disturbed him during this pilgrimage. When he finally reached the Church of the Holy Sepulchre,

He saw many forbidden and wicked things occurring there… so he sought out the patriarch of the holy church of Jerusalem and asked why gentiles and evil men were able to pollute holy places and steal away offerings from the faithful, using the church as if a stable, beating up Christians, despoiling pilgrims through unjust fees, and inflicting on them many sufferings." The frustrated patriarch threw up his hands in exasperation: "Why do you reprimand me and disturb me in the midst of my fatherly cares? I have but the strength and power of a tiny ant when compared to those proud men. We have to redeem our lives here by regular tribute payments (jizya) or else face death-dealing punishment."

This experience caused Peter to preach inflammatory statements about the Turks to upset Christians. However, doubts remain whether he ever made such a journey.

Sources differ as to whether Peter the Hermit was present at Pope Urban II's Council of Clermont in 1095, where the Pope made his military strategy for the First Crusade public. It is certain that he was one of the preachers of the armed pilgrimage in France afterwards, and his own experience may have helped to give fire to the Roman Catholic cause. Tradition in Huy holds that he was there when the call for war was announced and he began his preaching at once. He soon leapt into fame as an emotional revivalist, and the vast majority of sources and historians agree that thousands of serfs and peasants eagerly took the cross at his bidding, partly because of promises he did make.

This part of the First Crusade was also known as the Crusade of the Paupers. Peter organized and guided the paupers as a spiritually purified and holy group of pilgrims who would, supposedly, be protected by the Holy Ghost. Peter did not train his army, nor did he supply weapons or food. Some historians think it possible that the People's Crusade also included well-armed soldiers and nobles. (A list of known participants in Peter's army can be found at The Digital Humanities Institute.)