When most people think of laws today, they think of legislation passed by Congress. Yet, the primary source of law that governs society today developed from common law. In a common law legal system, laws are developed by judges through decisions of courts and similar tribunals, rather than by legislation. A majority of the rules of contract law, tort law, property law, and criminal law evolved from common law, while legislation served to simply codify decisions or fill in areas not covered by case law.