Old Saxon, also known as Old Low German, is a Germanic language. It is the earliest recorded form of Low German, and was spoken in northern Germany from the first centuries CE until the 12th century by Saxon peoples.

In the 5th century CE, many Saxons, along with related peoples such as the Angles (whence England) and the Jutes, invaded the Celtic-held British Isles. After this emigration, the Old Saxon speech split into two distinct branches: Old English (also called Anglo-Saxon), spoken in Britain; and Low German, spoken on the continent.