The Medieval Inquisition never existed as a distinct office but instead individual inquisitors, who were usually Dominicans or Franciscans, were mandated by the Pope to combat heresy. The first letter giving such a mandate dates from 1231. Many early inquisitors were acting in response to the Catharist heresy in southern France. Pope Innocent III exhorted secular rulers to proceed against the Cathari, calling heresy high treason against God and thus equating it to high treason against temporal rulers, which warranted death. After a military campaign, called the Albigensian Crusade, inquisitors were sent in to police the area.

Neither the papal legislation nor the Acts of the Fourth Lateran Council in 1215, which set forth the campaign against heretics, mentioned the death penalty at all. However, since Roman times, heretics had been executed as traitors and this continued once heretics were handed over to secular authority. Called "relaxation to the secular arm", it only happened in the case of multiple offenders and unrepentant heretics. For others it was expected that they would be punished by confiscation of property, banishment, pilgrimages, public recantation, and so on.

Torture could be used but inquisitors were conservative about applying it. They also preferred not to hand over heretics to the secular arm if they could persuade the heretic to repent. For example, Bernard Gui, a famous inquisitor working in the area of Toulouse (in modern France), executed 42 people out of over 700 guilty verdicts in fifteen years of office.

See also Inquisition, the Spanish Inquisition and the Roman Inquisition.