Pope Sergius III was a pope of the Roman Catholic Church from 29 January 904 to 14 April 911. Because Sergius III was possibly the only pope known to have ordered the murder of another pope and the only pope to have fathered an illegitimate son who later became pope (John XI), his pontificate has been described as "dismal and disgraceful".

Sergius was the son of Benedictus and came from a noble Roman family. His tenure was part of a period of feudal violence and disorder in central Italy, when the Papacy was a pawn of warring aristocratic factions, often led by prominent women.

The pontificate of Sergius III, according to Liutprand of Cremona, was remarkable for the rise of what papal historians saw as a "pornocracy", or "rule of the harlots", a reversal of the natural order as they saw it, according to Liber pontificalis and a later chronicler who was also biased against Sergius III. This "pornocracy" was an age with women in power: Theodora, whom Liutprand characterized as a "shameless whore... [who] exercised power on the Roman citizenry like a man" and her daughter Marozia, the mother of Pope John XI (931–935) and reputed to be the mistress of Sergius III, largely upon a remark by Liutprand (see Brook link below).

Sergius III may refer to:

Pope Sergius could refer to: