Where does common law come from?

Prior to the Norman Conquest, there was a network of local courts administering law across England, with three main law 'areas', such as Wessex. The Normans began to institute a common law regime across England.

By the time of Heny II, the process of superseding the network of local courts was well under way. Henry established a practice whereby his officials regularly visited the counties to investigate the administration of the king's local representatives and to administer justice.

By the fourteenth century, this system had evolved into a set of King's Courts, which were now known as the common law courts, since they administered the law that was common to the whole realm.

As opposed to statutory law, common law is considered to be judge-made law. Each case is decided on the basis of the most relevant precedents, but if a direct precedent can not be found the judge 'discovers' the precedent by providing a judgement that seems most consistent with the existing body of common law - in other Words what the judge's predessors would have determined had the case arisen much earlier.