A common law right exists even when no law has been passed by a legislature to establish that right. The right exists because the courts of the common law jurisdiction have recognized it. A number of rights were recognized at common law, but in the US, in 2011, the term common law is often associated with common law marriage. Common law principles also govern certain aspects of US trademark law.
The term common law refers to legal precedent that has been developed in a court system, rather than through legislative action. In a common law system, cases are decided based on past court decisions. This kind of system developed in England and has greatly influenced the legal systems of countries, including the US, which were once governed by Great Britain. Common law rights, as a general rule, do not exist outside these countries.
One of the most frequent examples of a common law right arises from common law marriage. This is the relationship that arises when a couple lives together for a certain period of time and presents themselves as a married couple, though no formal wedding ceremony occurred and no marriage certificate was obtained. In jurisdictions that recognize common law marriages, this couple would be entitled to all the rights associated with a marriage. Common law marriage is not recognized in all jurisdictions, however, and consequently, no common law right would arise out of such a relationship in these places.
Another common law right arises from the use of a trademark. Most countries have a formal process to trademark an image or symbol, known as a mark, with a government. In the US, however, the right to use a trademark can be established if the trademark has been used for a long period of time, even without having been formally registered. In these circumstances, a company may prohibit another party from using their mark by proving that the mark has been in use and is associated with the company.
Unlike a registered trademark, which has explicit protection throughout the US, a common law trademark might only be protected in the region where the mark is commonly used. For instance, a New England company could register a symbol or logo as a trademark and have the right to keep other companies throughout the US from using it. If the company has a common law trademark, however, and only sells their products within New England, another company might be able to use that logo in a different part of the US.