The Salii, Salians, or Salian priests were the "leaping priests" of Mars in ancient Roman religion, supposed to have been introduced by King Numa Pompilius. They were twelve patrician youths dressed as archaic warriors with an embroidered tunic, a breastplate, a short red cloak (paludamentum), a sword, and a spiked headdress called an apex. They were charged with the twelve bronze shields called ancilia, which—like those of the Mycenaeans—resembled a figure eight. One of the shields was said to have fallen from heaven in the reign of King Numa and eleven copies were made to protect the identity of the sacred shield on the advice of the nymph Egeria, consort of Numa, who prophesied that wherever that shield was preserved, the people would be the dominant people of the earth.

Each year in March, the Salii made a procession round the city, dancing and singing the Carmen Saliare. Ovid, who relates the story of Numa and the heavenly ancilia in his Fasti, found the hymn and the Salian rituals outdated and hard to understand. During the Principate, by decree of the Senate, Augustus's name was inserted into the song. They ended the day by banqueting. "Table of the Salii" (Saliaris cena) became proverbial in Latin for a sumptuous feast. It is unclear whether the primary aim of the ritual was to protect Rome's army, although this is the traditional view.

King Tullus Hostilius is said to have established another collegium of Salii in fulfillment of a vow which he made in the second war with Fidenae and Veii. These Salii Collini were also twelve in number, chosen from the Patricians, and appeared to have been dedicated to the service of Quirinus.

The Salii are sometimes credited with the opening and closing of the war cycle which would last from March to October.

Saliī is the plural form of Salius, a noun and adjective that seem to derive from salīre ("to jump, to leap") and to be cognate with saltāre ("to dance, to jump"). They were sometimes known as the Palatine Salii (Salii Palatini) to distinguish them from the priests of Quirinius. They are also known in English as the Salians or the Salian Priests. The Salii Collini were also known as the Agonales or Agonenses.

According to legend, Numa Pompilius established the Salii Palatini, which honored the god Mars, while Tullus Hostilius established the Salii Collini which honored the god Quirinus.

An origin among the Etruscans is attributed to a founding by Morrius, king of Veii. The Salii are also given an origin in connection with Dardanus and the Samothracian Di Penates, and the Salius who came to Italy with Evander and in the Aeneid competed in the funeral games of Anchises. Indeed in book VIII of The Aeneid, while in the land of King Evander Aeneas is entertained by the Salii during a feast, who are commemorating the fame and feasts of Hercules.

Ancient authors quoted by Maurus Servius Honoratus and Macrobius recorded that Salii had existed at Tibur, Tusculum and Veii even before their creation in Rome.