Witness protection is security provided to a threatened person providing testimonial evidence to the justice system, including defendants and other clients, before, during, and after trials, usually by police. While witnesses may only require protection until the conclusion of a trial, in particularly extreme cases, some witnesses are provided with new identities and may live out the rest of their lives under government protection. Protection is typically needed when their safety is at risk due to the potential for retaliation. The program aims to ensure their safety and encourage them to cooperate with law enforcement by providing information that can help solve cases and bring criminals to justice. It is an important tool in maintaining the integrity of the justice system and protecting those who are willing to come forward with crucial information.

Witness protection is usually required in trials against organized crime, where law enforcement sees a risk for witnesses to be intimidated by colleagues of defendants. It is also used at war crime, espionage and national security issues trials.

Not all countries have formal witness protection programs; instead, local police may implement informal protection as the need arises in specific cases. The programs provide support, sometime even including financial support and counseling, to help witnesses rebuild their lives. It's an important measure in safeguarding the well-being of those who come forward to assist in the pursuit of justice.

The Australian Federal Police administers the National Witness Protection Program under The National Witness Protection Act 1994, which delivers protection and assistance to witnesses and others identified as being at risk. Not all witnesses are eligible for the Witness Protection Program. The decision to admit a witness into the program is made on a case-by-case basis and involves a rigorous assessment process.

Canada's Witness Protection Program Act received royal assent on June 20, 1996. The program is run by the Royal Canadian Mounted Police (RCMP), with support by all levels of government and police forces. The program takes into account the unique circumstances of each case and tailors its approach to meet the specific needs of the witness and their situation. Similar to other countries, the WPP provides participants with new identities, including new name and documents. It also offers relocation assistance to ensure their safety.

Several departments of the Security Bureau of Hong Kong have specialized units to provide protection for witnesses and their families who face threats to their life. Notable units include the Witness Protection Unit (WPU) of the Hong Kong Police Force, the Witness Protection and Firearms Section (R4) of the ICAC, and the WPU of the Hong Kong Customs.

The members of these units undergo training in protection, firearms, self-defence, physical and tactical training. They are mostly trained in the use of, and issued, the Glock 19 compact handgun as sidearm. The standard Glock 17 or the long arms such as the Heckler & Koch MP5 sub-machine gun or the Remington Model 870 shotgun may be issued if the witness faces bigger threats. A new identity could be given to a witness, and the government may relocate them far from Hong Kong if the witness is still being threatened after the end of the trial.

In 2006, Indonesia enacted the Law n. 13 on Witness and Victim Protection, which introduced for the first time the legal qualifications of witness, (crimes) victim, complainant and justice collaborator within the Indonesian Criminal Procedure Code (KUHAP). In Indonesia, justice collaborators play an important role especially for the activities of the Corruption Eradication Commission, since "corruption in Indonesia is committed collectively".