been served." Ibid. In operation, the Rule did not have the deterrent effect expected by its drafters. See Advisory Committee Note on Rule 11, 28 U. S. C. App., pp. 575-576. The Advisory Committee identified two problems with the old Rule. First, the Rule engendered confusion regarding when a pleading should be struck, what standard of conduct would make an attorney liable to sanctions, and what sanctions were available. Second, courts were reluctant to impose disciplinary measures on attorneys, see ibid., and attorneys were slow to invoke the Rule. Vairo, Rule 11: A Critical Analysis, 118 F. R. D. 189, 191 (1988).

To ameliorate these problems, and in response to concerns that abusive litigation practices abounded in the federal courts, the Rule was amended in 1983. See Schwarzer, Sanctions Under the New Federal Rule 11-A Closer Look, 104 F. R. D. 181 (1985). It is now clear that the central purpose of Rule 11 is to deter baseless filings in district court and thus, consistent with the Rules Enabling Act's grant of authority, streamline the administration and procedure of the federal courts. See Advisory Committee Note on Rule 11, 28 U. S. C. App., p. 576. Rule 11 imposes a duty on attorneys to certify that they have conducted a reasonable inquiry and have determined that any papers filed with the court are well grounded in fact, legally tenable, and "not interposed for any improper purpose." An attorney who signs the paper without such a substantiated belief "shall" be penalized by "an appropriate sanction." Such a sanction may, but need not, include payment of the other parties' expenses. See ibid. Although the Rule must be read in light of concerns that it will spawn satellite litigation and chill vigorous advocacy, ibid., any interpretation must give effect to the Rule's central goal of deterrence.

III

We first address the question whether petitioner's dismissal of its antitrust complaint pursuant to Rule 41(a)(1)(i)

deprived the District Court of the jurisdiction to award attorney's fees.

Rule 41(a)(1) states:

"(1) By Plaintiff; by Stipulation. Subject to the provisions of Rule 23(e), of Rule 66, and of any statute of the United States, an action may be dismissed by the plaintiff without order of court (i) by filing a notice of dismissal at any time before service by the adverse party of an answer or of a motion for summary judgment, whichever first occurs, or (ii) by filing a stipulation of dismissal signed by all parties who have appeared in the action. Unless otherwise stated in the notice of dismissal or stipulation, the dismissal is without prejudice, except that a notice of dismissal operates as an adjudication upon the merits when filed by a plaintiff who has once dismissed in any court of the United States or of any state an action based on or including the same claim.”

Rule 41(a)(1) permits a plaintiff to dismiss an action without prejudice only when he files a notice of dismissal before the defendant files an answer or motion for summary judgment and only if the plaintiff has never previously dismissed an action “based on or including the same claim." Once the defendant has filed a summary judgment motion or answer, the plaintiff may dismiss the action only by stipulation, Rule 41(a)(1)(ii), or by order of the court, "upon such terms and conditions as the court deems proper," Rule 41(a)(2). If the plaintiff invokes Rule 41(a)(1) a second time for an "action based on or including the same claim," the action must be dismissed with prejudice.

Petitioner contends that filing a notice of voluntary dismissal pursuant to this Rule automatically deprives a court of jurisdiction over the action, rendering the court powerless to impose sanctions thereafter. Of the Courts of Appeals to consider this issue, only the Court of Appeals for the Second Circuit has held that a voluntary dismissal acts as a jurisdictional bar to further Rule 11 proceedings. See Johnson

Chemical Co. v. Home Care Products, Inc., 823 F. 2d 28, 31 (1987).

The view more consistent with Rule 11's language and purposes, and the one supported by the weight of Circuit authority, is that district courts may enforce Rule 11 even after the plaintiff has filed a notice of dismissal under Rule 41(a)(1). See Szabo Food Service, Inc. v. Canteen Corp., 823 F. 2d 1073, 1076-1079 (CA7 1987), cert. dism'd, 485 U. S. 901 (1988); Greenberg v. Sala, 822 F. 2d 882, 885 (CA9 1987); Muthig v. Brant Point Nantucket, Inc., 838 F. 2d 600, 603-604 (CA1 1988). The district court's jurisdiction, invoked by the filing of the underlying complaint, supports consideration of both the merits of the action and the motion for Rule 11 sanctions arising from that filing. As the "violation of Rule 11 is complete when the paper is filed," Szabo Food Service, Inc., supra, at 1077, a voluntary dismissal does not expunge the Rule 11 violation. In order to comply with Rule 11's requirement that a court "shall" impose sanctions “[i]f a pleading, motion, or other paper is signed in violation of this rule," a court must have the authority to consider whether there has been a violation of the signing requirement regardless of the dismissal of the underlying action. In our view, nothing in the language of Rule 41(a)(1)(i), Rule 11, or other statute or Federal Rule terminates a district court's authority to impose sanctions after such a dismissal.

It is well established that a federal court may consider collateral issues after an action is no longer pending. For example, district courts may award costs after an action is dismissed for want of jurisdiction. See 28 U. S. C. § 1919. This Court has indicated that motions for costs or attorney's fees are "independent proceeding[s] supplemental to the original proceeding and not a request for a modification of the original decree." Sprague v. Ticonic National Bank, 307 U. S. 161, 170 (1939). Thus, even "years after the entry of a judgment on the merits" a federal court could consider an award of counsel fees. White v. New Hampshire Dept. of

Employment Security, 455 U. S. 445, 451, n. 13 (1982). A criminal contempt charge is likewise "a separate and independent proceeding at law'" that is not part of the original action. Bray v. United States, 423 U. S. 73, 75 (1975), quoting Gompers v. Bucks Stove & Range Co., 221 U. S. 418, 445 (1911). A court may make an adjudication of contempt and impose a contempt sanction even after the action in which the contempt arose has been terminated. See United States v. Mine Workers, 330 U. S. 258, 294 (1947) ("Violations of an order are punishable as criminal contempt even though . . . the basic action has become moot"); Gompers v. Bucks Stove & Range Co., supra, at 451 (when main case was settled, action became moot, "of course without prejudice to the power and right of the court to punish for contempt by proper proceedings"). Like the imposition of costs, attorney's fees, and contempt sanctions, the imposition of a Rule 11 sanction is not a judgment on the merits of an action. Rather, it requires the determination of a collateral issue: whether the attorney has abused the judicial process, and, if so, what sanction would be appropriate. Such a determination may be made after the principal suit has been terminated.

Because a Rule 11 sanction does not signify a district court's assessment of the legal merits of the complaint, the imposition of such a sanction after a voluntary dismissal does not deprive the plaintiff of his right under Rule 41(a)(1) to dismiss an action without prejudice. "[D]ismissal . . . without prejudice" is a dismissal that does not "operat[e] as an adjudication upon the merits," Rule 41(a)(1), and thus does not have a res judicata effect. Even if a district court indicated that a complaint was not legally tenable or factually well founded for Rule 11 purposes, the resulting Rule 11 sanction would nevertheless not preclude the refiling of a complaint. Indeed, even if the Rule 11 sanction imposed by the court were a prohibition against refiling the complaint (assuming that would be an "appropriate sanction" for Rule 11 purposes), the preclusion of refiling would be neither a consequence of the

dismissal (which was without prejudice) nor a "term or condition" placed upon the dismissal (which was unconditional), see Rule 41(a)(2).

The foregoing interpretation is consistent with the policy and purpose of Rule 41(a)(1), which was designed to limit a plaintiff's ability to dismiss an action. Prior to the promulgation of the Federal Rules, liberal state and federal procedural rules often allowed dismissals or nonsuits as a matter of right until the entry of the verdict, see, e. g., N. C. Code § 1-224 (1943), or judgment, see, e. g., La. Code Prac. Ann., Art. 491 (1942). See generally Note, The Right of a Plaintiff to Take a Voluntary Nonsuit or to Dismiss His Action Without Prejudice, 37 Va. L. Rev. 969 (1951). Rule 41(a)(1) was designed to curb abuses of these nonsuit rules. See 2 American Bar Association, Proceedings of the Institute on Federal Rules, Cleveland, Ohio, 350 (1938) (Rule 41(a)(1) was intended to eliminate "the annoying of a defendant by being summoned into court in successive actions and then, if no settlement is arrived at, requiring him to permit the action to be dismissed and another one commenced at leisure") (remarks of Judge George Donworth, member of the Advisory Committee on Rules of Civil Procedure); id., at 309; see also 9 C. Wright & A. Miller, Federal Practice and Procedure § 2363, p. 152 (1971). Where state statutes and common law gave plaintiffs expansive control over their suits Rule 41(a)(1) preserved a narrow slice: It allowed a plaintiff to dismiss an action without the permission of the adverse party or the court only during the brief period before the defendant had made a significant commitment of time and money. Rule 41(a)(1) was not designed to give a plaintiff any benefit other than the right to take one such dismissal without prejudice.

Both Rule 41(a)(1) and Rule 11 are aimed at curbing abuses of the judicial system, and thus their policies, like their language, are completely compatible. Rule 41(a)(1) limits a litigant's power to dismiss actions, but allows one dismissal without prejudice. Rule 41(a)(1) does not codify any policy