Pope Zosimus (Italian: Zosimo; died 27 December 418) is the head of the Catholic Church from 18 March 417 to his death in 418.

He was born in Mesoraca, Calabria.

He succeeds Innocent I and is followed by Boniface I. Zosimus takes a decided part in the protracted dispute in Gaul as to the jurisdiction of the See of Arles over that of Vienne, giving energetic decisions in favor of the former, but without settling the controversy.

His fractious temper colors all the controversies in which he takes part, in Gaul, Africa and Italy, including Rome, where at his death the clergy are very much divided.

According to the Liber Pontificalis, Zosimus was a Greek and his father's name was Abram.

Historian Adolf von Harnack deduced from this that the family was of Jewish origin, but this cannot be certain.

Nothing is known of the life of Zosimus before his elevation to the Papal See.

His consecration as Bishop of Rome takes place on March 18, 417.

The festival is attended by Patroclus, Bishop of Arles, who had been raised to that See in place of Bishop Heros of Arles, who had been forcibly and unjustly removed by the imperial general Constantine.

Patroclus gains the confidence of the new pope at once; as early as 22 March he receives a papal letter which confers upon him the rights of a metropolitan over all the bishops of the Gallic provinces of Viennensis and Narbonensis I and II.

In addition, he is made a kind of papal vicar for the whole of Gaul; no Gallic ecclesiastic being permitted to journey to Rome without bringing with him a certificate of identity from Patroclus.

In the year 400, Arles had been substituted for Trier as the residence of the chief government official of the civil Diocese of Gaul, the "Prefectus Praetorio Galliarum".

Patroclus, who enjoys the support of the commander Constantine, uses this opportunity to procure for himself the position of supremacy above mentioned, by winning over Zosimus to his ideas.

The bishops of Vienne, Narbonne and Marseille regards this elevation of the See of Arles as an infringement of their rights, and raise objections which occasion several letters from Zosimus.

The dispute, however, is not settled until the pontificate of Pope Leo I.