A plea bargain (also plea agreement or plea deal) is an agreement in criminal law proceedings, whereby the prosecutor provides a concession to the defendant in exchange for a plea of guilt or nolo contendere. This may mean that the defendant will plead guilty to a less serious charge, or to one of the several charges, in return for the dismissal of other charges; or it may mean that the defendant will plead guilty to the original criminal charge in return for a more lenient sentence.

A plea bargain allows both parties to avoid a lengthy criminal trial and may allow criminal defendants to avoid the risk of conviction at trial on a more serious charge. For example, in the legal system of the United States, a criminal defendant charged with a felony theft charge, the conviction of which would require imprisonment in state prison, may be offered the opportunity to plead guilty to a misdemeanor theft charge, which may not carry a custodial sentence.

In cases such as an automobile collision when there is a potential for civil liability against the defendant, the defendant may agree to plead "no contest" or "guilty with a civil reservation", which essentially is a guilty plea without admitting civil liability.

Plea bargaining can present a dilemma to defense attorneys, in that they must choose between vigorously seeking a good deal for their present client, or maintaining a good relationship with the prosecutor for the sake of helping future clients. However, in the case of the US for example, defense attorneys are required by the ethics of the bar to defend the present client's interests over the interests of others. Violation of this rule may result in disciplinary sanctions being imposed against the defense attorney by the appropriate state's bar association.

In charge bargaining, defendants plead guilty to a less serious crime than the original charge that was filed against them. In count bargaining, they plead guilty to a subset of multiple original charges. In sentence bargaining, they plead guilty agreeing in advance what sentence will be given; however, this sentence can still be denied by the judge. In fact bargaining, defendants plead guilty but the prosecutor agrees to stipulate (i.e., to affirm or concede) certain facts that will affect how the defendant is punished under the sentencing guidelines.

Plea bargaining was considered a predominantly American phenomenon during the 1970s, but has since spread throughout the world.