In countries adopting the common law adversarial system, the prosecutor is the chief legal representative of the prosecution. The prosecution is the legal party responsible for presenting the case against an individual suspected of breaking the law in a criminal trial.

Prosecutors are typically lawyers who possess a university degree in law, are recognized as legal professionals by the court in which they intend to represent the state, and, in countries where the distinction is made, are barristers. They usually only become involved in a criminal case once charges need to be laid and are typically employed by an office of the government with safeguards in place to ensure such an office can successfully pursue the prosecution of government officials. Often multiple offices exist in a single country due to the various legal jurisdictions that exist.

In the United Kingdom, Australia and Canada the director of any such office is typically known as the Director of Public Prosecutions and is appointed (as opposed to elected).