Rarely. There's a popular misconception that embalming, in which a body is treated to slow its disintegration, is always required by law after death. In fact, no state requires routine embalming and some don't require it at all. Embalming is legally required only in special circumstances, such as:
when a body will be transported by plane or train from one state or country to another.
when there's a relatively long time -- a week or more -- between the death and the burial or cremation.
in some cases, where the death occurred because of a communicable disease.
If you have a question about whether embalming is required in a particular instance, contact your local funeral or memorial society for help.
A brief look into the history of embalming in the United States helps explain how it took hold here. Originally shunned as barbaric and paganistic, the practice first gained popularity during the Civil War, when bodies of the war dead were transported over long distances. When that war ended, embalming was promoted -- mostly by those who performed the service -- as an essential means of preserving dead bodies and keeping them hygienic.
For most people in most circumstances, refrigerating the body serves the same purpose of slowing decomposition, and it's usually just as effective for short periods. The biggest difference is the length of time a body can be preserved: A body that's been refrigerated before being buried will begin decomposing within days; an embalmed body begins decomposing within weeks.
To underscore this reality, a law called the Funeral Rule, which is enforced by the Federal Trade Commission, prohibits funeral providers from claiming that investing in either embalming or particular types of caskets will preserve bodies indefinitely. The rule also requires providers to inform consumers that embalming isn't required by law. And it dictates that embalming can't be performed without prior written permission from the person responsible for making the final arrangements.
Embalming, followed by various cosmetic enhancements, is still generally performed when there will be an open casket or public viewing of the body. However, the practice is frowned upon or prohibited by a number of religious dictates, including traditional Jewish, Muslim, and Baha'i faiths.