After immigration agents found marijuana in respondent Ruiz's luggage, federal prosecutors offered her a "fast track" plea bargain, whereby she would waive indictment, trial, and an appeal in exchange for a reduced sentence recommendation. Among other things, the prosecutors' standard "fast track" plea agreement acknowledges the Government's continuing duty to turn over information establishing the defendant's factual innocence, but requires that she waive the right to receive impeachment information relating to any informants or other witnesses, as well as information supporting any affirmative defense she raises if the case goes to trial. Because Ruiz would not agree to the latter waiver, the prosecutors withdrew their bargaining offer, and she was indicted for unlawful drug possession. Despite the absence of a plea agreement, Ruiz ultimately pleaded guilty. At sentencing, she asked the judge to grant her the same reduced sentence that the Government would have recommended had she accepted the plea bargain. The Government opposed her request, and the District Court denied it. In vacating the sentence, the Ninth Circuit took jurisdiction under 18 U. S. C. § 3742; noted that the Constitution requires prosecutors to make certain impeachment information available to a defendant before trial; decided that this obligation entitles defendants to the information before they enter into a plea agreement; ruled that the Constitution prohibits defendants from waiving their right to the information; and held that the "fast track" agreement was unlawful because it insisted upon such a waiver.