Desuetude is a word derived from the Latin meaning “to fall into discuse.” In the law, it specifically refers to laws that still technically stand on the books but are deemed invalid and unenforceable because they have not been applied in an extended period of time. Legal attitudes about obsolete laws vary between nations and legal systems, and in some regions there is a push to remove these laws from the legal code altogether for the sake of organization, rather than allowing them to stand unenforced.
Laws enter desuetude for a wide variety of reasons. Sometimes society collectively agrees to stop enforcing laws because they are a reflection of outdated ideas; in the United States, for example, a number of laws concerning sexual practices remain on the books, but are no longer enforced. The passage of another law can also render an existing law obsolete without specifically striking it from the books or changing it. Other laws were sporadically enforced when first introduced and gradually fell out of favor.
When a law falls into disuse, it is common for awareness of the law to fade as well. Law enforcement officers may not realize that particular activities are covered in the legal code and can be grounds for arrest and penalties, for example, and lawyers and judges may not be familiar with the applications of the law. Over time, a law reaches the state of desuetude and while it is legally present, it is never enforced.
Some legal systems encourage the addition of sunset clauses to legislation, allowing legislation to be canceled and struck from the books if it reaches the state of desuetude. In these cases, when the law is set to expire, people have the option of renewing it, or allowing the sunset clause to lapse. This tactic is also used for controversial laws where legislators fear they will not be able to pass a permanent law, but may be able to make a law effectively permanent by extending each time it seems about to expire.
If people can demonstrate that a law is in desuetude, they can petition legislators and other authorities to consider striking it from the books. This is sometimes encouraged with laws concerning morality where there are concerns about how the law reflects on society; anti-miscegenation laws, for example, are considered racist in many regions and people may want to remove the laws from the legal code to send a clear message to society.