Common law
The common lawso named because it was "common" to all the king's courts across Englandoriginated in the practices of the courts of the English kings in the centuries following the Norman Conquest in 1066. Prior to the Norman Conquest, much of England's legal business took place in the local folk courts of its various shires and hundreds. A variety of other individual courts also existed across the land: urban boroughs and merchant fairs held their own courts, as did the universities of Oxford and Cambridge, and large landholders also held their own manorial and seigniorial courts as needed. Additionally, the Catholic Church operated its own court system that adjudicated issues of canon law.
Unjust enrichment
In systems of law derived from the English common law, the historical core of the law of unjust enrichment lies in quasi-contract. These were common law (as distinct from equitable) claims giving rise to a personal liability to pay the money value of a benefit received from another. Legal scholars from Oxford, Cambridge and Harvard at the turn of the 20th century began to rationalise these disparate actions into a coherent body of law. The principle said to underlie these actions was eventually recognized as unjust enrichment. Subsequent scholarship has sought to expand the explanatory power of the principle of unjust enrichment and it is now often said (albeit not without controversy) to encompass both common law and equitable claims.