Attacotti, Atticoti, Attacoti, Atecotti, Atticotti, and Atecutti were Latin names for a people first recorded as raiding Roman Britain between 364 and 368, alongside the Scoti, Picts, Saxons, Roman military deserters and the indigenous Britons themselves. The marauders were defeated by Count Theodosius, father of Roman Emperor Theodosius I, in 368.

The exact origins of the Attacotti and the extent of their territory are uncertain, although historians usually place them in either Scotland or Ireland. In about 400, Roman units recruited among the Attacotti were recorded in the Notitia Dignitatum, and one tombstone of a soldier identified as such is known. Their existence as a distinct people is given additional credence by two incidental claims that they practised cannibalism and polyandry (taking multiple husbands) in the writings of Saint Jerome.

The historian Ammianus provides an account of the tumultuous situation in Britain between 364 and 369, and he describes a corrupt and treasonous administration, native British troops (the Areani) in collaboration with the barbarians, and a Roman military whose troops had deserted and joined in the general banditry. The situation arose as a consequence of the failed imperial power-grab (350–353) by Magnentius (303–353), followed by a bloody and arbitrary purge conducted by Paulus Catena in an attempt to root out potential sympathisers of Magnentius in Britain, and aggravated by the political machinations of the Roman administrator Valentinus.

Ammianus describes the marauders as bands moving from place to place in search of loot. Nevertheless, one Roman commander was killed in a pitched battle and another was taken prisoner in an ambush and killed. (See Great Conspiracy.) As there was no longer an effective military force in the province, a substantial one was sent from Gaul under Count Theodosius, who quickly and ruthlessly restored order. Theodosius then focused his efforts on the repair of political problems within the province.

The Notitia Dignitatum is a list of offices of the early 5th century Roman Empire, and includes the locations of the offices and the staff (including military units) assigned to them. The names of several auxilia palatina resemble that of the Attacotti who were mentioned by Ammianus, and in an 1876 publication, historian Otto Seeck assigned the name Atecotti to various spellings ("acecotti", "atecocti", "attecotti", "attcoetti", "[illegible]ti", and "arecotti") in the Notitia Dignitatum, and documented his assignments within the publication. This produced four conjectural occurrences of Atecotti-related units:

The discovery of a contemporary funerary dedication to a soldier of the "unit of Atecutti" (emended from "Ategutti") at Thessalonica, in the Roman Diocese of Illyricum, supports this reconstruction, as the Notitia Dignitatum places one Atecotti unit in that diocese.

St. Jerome was a Christian apologist whose writings contain two incidental references to the Attacotti. His account is particularly noteworthy because he was in Roman Gaul c. 365–369/70, while the Attacotti were known to be in Britain until 368 and may have entered Roman military service soon after. Thus it is credible that Jerome had seen Attacotti soldiers and had heard Roman accounts of the recent fighting in Britain.

In his Letter LXIX. To Oceanus, he is urging a responsible attitude towards marriage, at one point saying that one should not be "like the Scots [i.e., the Irish Scoti] and the Atacotti, and the people of Plato's Republic, to have community of wives and no discrimination of children, nay more, to be aware of any semblance even of matrimony".