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. The British Empire spread the English legal system to its historical colonies, many of which retain the common law system today. These "common law systems" are legal systems that give great precedential weight to common law, and to the style of reasoning inherited from the English legal system.
Law of the Republic of Ireland
Ireland was the subject of the first extension of England's common law legal system outside England. While in England the creation of the common law was largely the result of the assimilation of existing customary law, in Ireland the common law was imported from England supplanting the customary law of the Irish. This, however, was a gradual process which went hand-in-hand with English (and later, British) influence in Ireland.