Annales Bertiniani (or Annals of Saint Bertin) are late Carolingian, Frankish annals that were found in the Abbey of Saint Bertin, Saint-Omer, France, after which they are named. Their account is taken to cover the period 830-82, thus continuing the Royal Frankish Annals (741-829), from which, however, it has circulated independently in only one manuscript. They are available in the Monumenta Germaniæ Historica (Waitz 1883) and in a later French edition taking into account a newly discovered manuscript (Grat 1964). The Annals of St. Bertin are one of the principal sources of ninth-century Francia, and are particularly well-informed on events in the West Frankish sphere of Charles the Bald. The Annales Fuldenses are usually read as an East Frankish counterpart to their narrative.
It has been suggested that the annals were first written by scribes in the court of Louis the Pious. There is no doubt that they were later continued as an independent narrative, eventually becoming somewhat emancipated from the Palace since the early 840s, first by Prudentius of Troyes (+861) and thereafter Hincmar of Reims (until 882), on whose lost manuscript their tradition is almost entirely dependent. Moreover, there are strong hints that the original text of the annals underwent at least minor changes under the latter's supervision. 
The annals' account is mostly first-hand and includes documents such as papal letters and excerpts from conciliar acts.
The text is characterized by the struggles between the Carolingians, their relations to the Holy Roman Church - "sancta romana ecclesia" - and as well the raids from neighbouring regions. Amongst these last are the practically annual reports of raids carried out by various warrior-bands from Scandinavia - who are now popularly known as Vikings.
During the ninth century, these warrior-bands regularly laid waste to the lands of the Frisians, sailed up rivers like the Seine, Loire, and Rhine, where they caused great devastation in the country, and plundered Carolingian monasteries and episcopal cities. After 841, only in the years 874 and 875 are there no references to Viking activity. There is much to read in the annals, and the narrative sheds also some light on the many incidents that form the scenario in which Scandinavians came to more formal, i.e. diplomatic and ecclesiastic, relations with their southern neighbours - for example the Normans' fealty to King Charles III of West Francia in 911.
The concentration on ecclesiastic centres, which presumably housed vast amounts of movable wealth, has led some historians to believe that contemporary source writers, i.e. clergymen - including Prudentius and Hincmar, which are believed to have had at least editorial influence on the annals - exaggerated their accounts of the raids because they were usually the invaders' primary targets and frequently had to foot the bill when kings agreed to pay the Vikings off, as Charles the Fat did at the Siege of Paris in 885-6.  Most scholars now believe the Vikings posed little more than a persistent, niggling military threat to the Carolingian regime. 
The annals are notable, among other things, for containing one of the earliest written references to Rus'.  According to the annals, a group of followers to the emissaries from Constantinople was presented through a letter handed over to the emperor by the emissaries. The letter stated that they called themselves Rhos - "qi se, id est gentem suam, Rhos vocari dicebant" - and had journeyed to Constantinople; but now they were fearful to return home, because the roads they had travelled were not safe. They had therefore set out with the Byzantine embassy hoping to obtain the Franks' assent for travelling via Germany. At Ingelheim royal residence, near Mainz, they were queried by Frankish Emperor Louis the Pious, as he suspected they might be on reconnaissance (Latin: exploratores), and they could assure him in the rationale for their northern destination, as they belonged to the Sueones: "eos gentis esse Sueonum". He decided to keep them by him until it could be ascertained for sure whether they had come in earnest purpose or not, and they are not mentioned again in the annals. This incident is mentioned under the year 839.
A still ongoing polemic involves the phrase "rex illorum Chacanus" (Waitz 1883, pp. 19-20), "rex illorum Chaganos" (Rau 1980, p. 44). The phrase belongs to the written presentation to the emperor, and in context names the king of the Rus'; king Chacanus or Chaganos. Garipzanov (2006) has recently made observations on the likelihood that chacanus is the correct, i.e. original term. The traditional interpretation is that 'rex illorum Chacanus' is meant to be understood as khagan, not actually a person's name, but instead an entirely foreign kind of sovereignty. However, there is an alternative interpretation, that Chacanus is a Latin transcription of the Scandinavian proper name Håkan since in mainstream scholarship the Rus' people, who lived in northern Russia, had their ancestral homeland in Sweden. Garipzanov holds to the latter and finds that the form 'chacanus' is a unique occurrence in Frankish sources; variants hereof, in the Carolingian sources, that do signify the foreign form of sovereignty are caganus, chagan, kagan and also chaganum. Scholars have also sought to establish a connection between the Rus'-Byzantine embassy to Louis the Pious and contemporary events in the Eastern Empire, as recorded in the Life of St. George of Amastris, one of the earliest Greek sources on the Rus'.
The narrative came to an end in 882 when an elderly, frail Hincmar was forced to flee his cathedral at Reims from approaching Viking invaders.  The scholar-bishop died shortly after at Épernay, and the narrative was not continued.
The annals is one of five major independent narrative accounts of the late 9th century. The others are: