The U.S. Supreme Court's decision in Haring v. Prosise is identified as having stopped the pendulum from swinging to preclusion on an issue of the admissibility of evidence in a trial that was waived by a plea of guilty. Cases that have considered this same problem are divided into three categories. In the first, the criminal defendant comes into court as a civil claimant, seeking relief on a theory turning in some way on the nonexistence of an essential element of the case; in the second, the criminal defendant is a defendant in a subsequent civil proceeding, and the party seeking recovery is the government that initiated prior criminal prosecution; and in the third, the criminal defendant is a civil defendant in an action brought by a third party, in which his defense (or the third party's claim) turns in whole or in part on some essential element of the crime. Each category is identified as having a rough validity, but the strongest candidates for preclusion are said to be within the third category. The difference between the acceptance of a guilty plea in a criminal proceeding and in a civil case is distinguished, and difficulties arising with the use of the nolo contendere plea are addressed. A guilty plea, given its consequences and the degree of judicial involvement, is concluded to be more than an ordinary admission; the importance of it being recognized as such is emphasized. Included is a list of 112 references.