common law is based on the decisions made by judges in past court cases. it comes from england and it became part of almost every country that once belonged to the british empire, except malta, scotland, the u.s. state of louisiana, and the canadian province of quebec. it is also the predominant form of law in the united states, where many laws called statutes are written by congress, but many more legal rules exist from the decisions of the courts. common law had its beginnings in the middle ages, when king john was forced by his barons to sign a document called the magna carta.