Guilty pleas account for an estimated 90 percent of all criminal convictions secured in the United States. Many defendants enter such pleas because they are guilty and do not wish to prolong the criminal process, but other defendants or their attorneys negotiate to secure concessions as to the charge or sentence in return for entering the guilty plea. The Supreme Court has played a significant part in legitimating open plea bargaining. The first relatively recent case in which the guilty plea was the pivotal issue dates from the 1969 holding in Boykin v. Alabama. This decision broke new ground in imposing a substantial part of rule 11 of the Federal Rules of Criminal Procedure on the States under the due process clause. Other important rulings followed in the 1970 cases of McMann v. Richardson and Parker v. North Carolina. In the first case, the Court held that a jury will not be permitted to learn of any confession if the trial judge rules it to be coerced. In the Parker case, the use of coerced confessions in determining a guilty plea was held unconstitutional. In Santobello v. New York (1971), the Court specifically upheld the legality of plea bargaining as to both charge and sentence recommendations. The 1978 decision in Bordenkircher v. Hayes carried the trend in plea bargaining case law a step further. In that case, the Court held that the prosecutor was entitled to bargain hard in encouraging guilty pleas in an effort to expedite the criminal process. The net effect of these cases is to make plea bargaining legitimate. Except in unusual cases, both parties must abide by the bargain struck if there is a factual basis for the pleas. Seventy-five footnotes are provided.