The Heptarchy (Greek: seven + realm) is a collective name applied to the Anglo-Saxon kingdoms of south, east, and central Great Britain during late antiquity and the early Middle Ages, conventionally identified as seven: Northumbria, Mercia, East Anglia, Essex, Kent, Sussex and Wessex.

The Anglo-Saxon kingdoms eventually unify into the Kingdom of England.The term has been in use since the 16th century, but the initial idea that there were seven Anglo-Saxon kingdoms is attributed to the English historian Henry of Huntingdon in the 12th century and was first used in his Historia Anglorum.

By convention the label is considered to cover the period from 500 to 850, often referred to as the Dark Ages, which approximately represents the period following the departure of Roman legions from Britain until the kingdoms came under the overlordship of Egbert of Wessex.Though heptarchy suggests the existence of seven kingdoms, the number fluctuates, as kings contend for supremacy at various times within the conventional period.

In the late sixth century, the king of Kent is a prominent lord in the south; in the seventh century the rulers of Northumbria and Wessex are powerful; in the eighth century Mercia achieves hegemony over the other surviving kingdoms.

Yet as late as the reigns of Eadwig and Edgar (955–75), it is still possible to speak of separate kingdoms within the English population.Recent research has revealed that some of the Heptarchy kingdoms (notably Essex and Sussex) did not achieve the same status as the others.

Conversely, there also existed alongside the seven kingdoms a number of other political divisions which played a more significant role than previously thought.

Such were the kingdoms (or sub-kingdoms) of: Bernicia and Deira within Northumbria; Lindsey in present-day Lincolnshire; the Hwicce in the southwest Midlands; the Magonsæte or Magonset, a sub-kingdom of Mercia in what is now Herefordshire; the Wihtwara, a Jutish kingdom on the Isle of Wight, originally as important as the Cantwara of Kent; the Middle Angles, a group of tribes based around modern Leicestershire, later conquered by the Mercians; the Hæstingas (around the town of Hastings in Sussex); and the Gewisse, a Saxon tribe in what is now southern Hampshire later developing into the kingdom of Wessex.