Marianus Scotus (1028–1082 or 1083) was an Irish monk and chronicler.
Marianus Scotus is Latin for "Marian the Scot", although that term at the time was still inclusive of the Irish. He is sometimes known as Marianus Scotus of Mainz to distinguish him from Marianus Scotus of Regensburg and sometimes called Máel Brigte (Modern Irish: Maelbhríde), "Brigit's Servant".
An Irishman by birth, he was educated by a certain Tigernach and, having become a monk in 1052, he crossed over to the continent of Europe in 1056, and his subsequent life was passed in the abbeys of St Martin at Cologne and of Fulda, and at Mainz. He died at Mainz, on December 22, 1082 or 1083, and was buried in Mainz Cathedral.
Marianus wrote a Clear Chronicle (Latin: Cronica Clara), which purports to be a universal history from the creation of the world to 1082 and which employed a dual numbering scheme on the misunderstanding that the Christian era computed by Dionysius Exiguus had been mistaken by 22 years. The chronicle was very popular during the Middle Ages and, in England, was extensively used by John of Worcester and other writers. It was first printed at Basel in 1559 and has been edited with an introduction by Georg Waitz for the Monumenta Germaniae Historica: Scriptores, Vol. V.