The United States Department of Justice has a Witness Protection Program, in which a person who has given significant information about someone who is wanted for crimes is given a new identity in a new location. It may be used in the case of an innocent party who testified against, say, a member of The Mafia, but is often used to protect a member of organized crime who has done a Heel–Face Turn and testified for the government in court. To keep said witness from becoming either part of the concrete used to rebuild Exit 7 on the New Jersey Turnpike, or the main ingredient in Bark-O Dog Food, the Federal government provides them with a new place to live and a new identity.

This operation will be very expensive, and the party who has been granted relocation will be subject to significant restrictions. Usually, they will not be allowed contact with anyone from their past, may be required to change occupations, or have to do other things to protect their new identity from discovery by those who might harm them. If they cause their cover to be broken, it is extremely likely they will not receive a new one.

Once the person goes in, it's basically a one-way trip; there is no connection between them and their previous life. If they are wanted for crimes or leave behind debts prior to going into the program, they will not be reachable. The Justice Department has even told the IRS to get lost for the collection of unpaid taxes by someone who went into the program. So far, not a single person who has entered the US Federal Witness Protection program and followed all the rules properly has ever been killed (although the same cannot be said for people who don't follow the rules).

This idea can be used in fiction in a number of ways:

• If the protagonist goes into witness protection, expect focus on the hardships of the program. Frequently they were an innocent who has had to turn their life upside down because of someone else who is a threat to them; often they lost a loved one to the people they had to run away from (which may be why they were testifying in the first place).
• If it's someone the protagonist knows, it's a convenient way to have them Put on a Bus and lose all contact with the rest of the cast without actually killing them. Similarly, you can expect copious Angst about losing someone they cared about to witness protection (like a boyfriend or girlfriend losing their lover who follows his or her family into the program).
• It can also be approached from the other end: the protagonists start digging into someone's background, discover that it looks suspiciously fabricated and dig deeper under the assumption that they're a bad egg, and find themselves on the wrong end of a "back off" lecture from a US Marshal.
• The protectee might just blow the whole thing off and Ditch the Bodyguards, leading to exactly the kind of dangerous escapades everyone was trying to avoid in the first place.

Some states provide a similar (but less comprehensive, obviously) program for witnesses to state crimes. Other countries also have similar programs.

If someone starts over themselves, without government assistance, they are Starting a New Life.

If, despite everything, the bad guys still manage to find the person in question, then we have a Witless Protection Program.

A number of films have used the premise of witness protection, either as a story Ripped from the Headlines, being Based on a True Story, or total fiction. The trope can be used dramatically, or for comedy.

Subtrope of Sent Into Hiding.

Examples: