Old English (Ænglisc, Anglisc, Englisc) or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southern and eastern Scotland, more specifically in the England Old Period, between at least the mid-5th century and the mid-12th century. What survives through writing represents primarily the literary register of Anglo-Saxon.

It is a West Germanic language closely related to Old Frisian. Old English had a grammar similar in many ways to Classical Latin, and was much closer to modern German and Icelandic than modern English in most respects, including its grammar. It was fully inflected with five grammatical cases (nominative, accusative, genitive, dative, and instrumental), two grammatical numbers (singular and plural) and three grammatical genders (masculine, feminine, and neuter). First and second person personal pronouns also had dual forms for referring to groups of two people, in addition to the usual singular and plural forms. The instrumental case was somewhat rare and occurred only in the masculine and neuter singular; it could typically be replaced by the dative. Adjectives, pronouns and (sometimes) participles agreed with their antecedent nouns in case, number and gender. Finite verbs agreed with their subject in person and number.

The term Anglo-Saxon is used by some historians to designate the Germanic tribes who invaded and settled the south and east of Britain beginning in the early 5th century and the period from their creation of the English nation up to the Norman conquest. The Anglo-Saxon era denotes the period of English history between about 550 and 1066. The term is also used for the language, now known as Old English, that was spoken and written by the Anglo-Saxons and their descendants in England (and part of southeastern Scotland) between at least the mid-5th century and the mid-12th century.

The Benedictine monk Bede, writing in the early 8th century, identified the English as the descendants of three Germanic tribes:

Their language, Old English, which derived from Ingvaeonic West Germanic dialects, transformed into Middle English from the 11th century. Old English was divided into four main dialects: West Saxon, Mercian, Northumbrian and Kentish.

The term Anglo-Saxon can be found in documents produced in the time of Alfred the Great, who seems to have frequently used the titles rex Anglorum Saxonum and rex Angul-Saxonum (king of the English Saxons). The Old English terms ænglisc ('Angle-kin') and Angelcynn ('gens Anglorum') had already lost their original sense of referring to the Angles, as distinct from the Saxons, when they are first attested. In their earliest sense they referred to the nation of Germanic peoples who settled eastern Britain from the 5th century.^{[citation needed]} The indigenous Britons, who wrote in both Latin and Welsh, referred to these invaders as 'Saxones' or 'Saeson' – the word Saeson is the modern Welsh word for 'English people'; the equivalent word in Scottish Gaelic is Sasannach and in the Irish language, Sasanach.