The Norsemen (or Northmen) were a Germanic cultural group in the Early Middle Ages, originating among speakers of Old Norse in Scandinavia. During the late eighth century, Scandinavians embarked on a large-scale expansion in all directions, giving rise to the Viking Age. In English-language scholarship since the 19th century, Norse seafaring traders, settlers and warriors have commonly been referred to as Vikings.

Historians of Anglo-Saxon England often use the term "Norse" in a different sense, distinguishing between Norse Vikings (Norsemen) from Norway, who mainly invaded and occupied the islands north and north-west of Britain as well as Ireland and western Britain, and Danish Vikings, who principally invaded and occupied eastern Britain.

The word Norseman first appears in English during the early 19th century: the earliest attestation given in the third edition of the Oxford English Dictionary is from Walter Scott's 1817 Harold the Dauntless. The word was coined using the adjective norse, which was borrowed into English from Dutch during the 16th century with the sense 'Norwegian', and which by Scott's time had acquired the sense "of or relating to Scandinavia or its language, esp[ecially] in ancient or medieval times". As with modern use of the word viking, therefore, the word norseman has no particular basis in medieval usage.

The term Norseman does echo terms meaning 'Northman', applied to Norse-speakers by the peoples they encountered during the Middle Ages. The Old Frankish word Nortmann ("Northman") was Latinised as Normannus and was widely used in Latin texts. The Latin word Normannus then entered Old French as Normands. From this word came the name of the Normans and of Normandy, which was settled by Norsemen in the tenth century.

The same word entered Hispanic languages and local varieties of Latin with forms beginning not only in n-, but in l-, such as lordomanni (apparently reflecting nasal dissimilation in local Romance languages). This form may in turn have been borrowed into Arabic: the prominent early Arabic source al-Mas‘ūdī identified the 844 raiders on Seville not only as Rūs but also al-lawdh’āna.

The Anglo-Saxon Chronicle, written in Old English, distinguishes between the pagan Norwegian Norsemen (Norðmenn) of Dublin and the Christian Danes (Dene) of the Danelaw. In 942, it records the victory of King Edmund I over the Norse kings of York: "The Danes were previously subjected by force under the Norsemen, for a long time in bonds of captivity to the heathens".

In modern scholarship, Vikings is a common term for attacking Norsemen, especially in connection with raids and monastic plundering by Norsemen in the British Isles, but it was not used in this sense at the time. In Old Norse and Old English, the word simply meant 'pirate'.

The Norse were also known as Ascomanni, ashmen, by the Germans, Lochlanach (Norse) by the Gaels and Dene (Danes) by the Anglo-Saxons.