What is common law? Is it a type of law or just the name of that cable TV show about cops?
Well, actually, it's both. But the focus here will be more on the former (you can check out the latter on your own time).
Common law is one of the main systems of law in the United States -- the other main kind being civil law. With that said, what exactly is common law?
Common Law Is 'Case Law'
Common law is also known as case law, or case precedent (in Latin and in the legal world, this is also known as stare decisis). In other words, common laws are those based on judicial case rulings. Therefore, common laws might vary a lot, depending on what jurisdiction you are in.
Basically, when there's a case, and a judge rules a certain way, this becomes the basis for deciding future, similar cases.
Of course, common law is ever-changing -- think of recent trends like gay marriage and e-commerce law, for example. Every time a decision is overturned by a court or a more relevant, recent ruling is made, that becomes the new basis.
Some popular areas of the law that use common law include marriage laws in certain states, contract law, and laws about negligence, to name a few.
Civil Law Is Codified
Criminal law does not use common law. So if you're accused of robbery, your criminal defense lawyer likely won't focus on judicial precedents; rather, she'll research your state's statutes, which defines what robbery is and what the penalties are. If the case is less clear-cut, courts will still often look to prior cases -- common law -- for help. But in general, the statute is controlling.
The difference between civil and common law can be confusing, and even those in the legal profession sometimes have a hard time remembering and grasping what common law is, when it's used, and when it's not. An easy way to remember the difference: Common law (or case law) will always and only be made by judges (through court rulings), while all other types of law typically won't be, and can come from a variety of other sources.