Under the preceding Romano-British administration, the area of Kent faced repeated attacks from seafaring raiders during the fourth century CE, with Germanic-speaking foederati likely being invited to settle in the area as mercenaries. Following the end of Roman administration in 410, further linguistically Germanic tribal groups moved into the area, as testified by both archaeological evidence and Late Anglo-Saxon textual sources. The primary ethnic group to settle in the area appears to have been the Jutes, who established their Kingdom in East Kent, which was potentially initially under the dominion of the Kingdom of Francia. It has been argued that an East Saxon community initially settled West Kent, before being conquered by the expanding East Kentish in the sixth century.
The earliest recorded king of Kent was Æthelberht, who as bretwalda wielded significant influence over other Anglo-Saxon kingdoms in the late sixth century. The Christianization of the Anglo-Saxons began in Kent under Æthelberht's reign with the arrival of the monk Augustine of Canterbury and his Gregorian mission in 597. It was one of the seven traditional kingdoms of the so-called Anglo-Saxon heptarchy, but it lost its independence in the 8th century when it became a sub-kingdom of Mercia. In the 9th century, it became a sub-kingdom of Wessex, and in the 10th century, it became part of the unified Kingdom of England that was created under the leadership of Wessex. Its name has been carried forward ever since as the county of Kent.
Knowledge of Anglo-Saxon Kent comes from scholarly study of Late Anglo-Saxon texts such as the Anglo-Saxon Chronicle and the Ecclesiastical History of the English People, as well as archaeological evidence such as that left by Early Medieval cemeteries and settlements, and by the toponymical evidence of Kentish place-names.
In the Romano-British period, the area of modern Kent that lay east of the River Medway was a civitas known as Cantiaca. Its name had been taken from an older Common Brittonic place-name, Cantium ("corner of land" or "land on the edge") used in the preceding pre-Roman Iron Age, although the extent of this tribal area is unknown.
During the late third and fourth centuries, Roman Britain had been raided repeatedly by Franks, Saxons, Picts, and Scots. As the closest part of Britain to mainland Europe, it is likely that Kent would have experienced many attacks from seafaring raiders, resulting in the construction of four Saxon Shore Forts along the Kentish coast: Regulbium, Rutupiae, Dubris, and Portus Lemanis. It is also likely that Germanic-speaking mercenaries from northern Gaul, known as foederati, would have been hired to supplement official Roman troops during this period, with land in Kent as payment. These foederati would have assimilated into Romano-British culture, making it difficult to distinguish them archaeologically.