(c) Motion for Judgment on the Pleadings. After the pleadings are closed一but early enough not to delay trial一a party may move for judgment on the pleadings.
(d) Result of Presenting Matters Outside the Pleadings. If, on a motion under Rule 12(b)(6) or 12(c), matters outside the pleadings are presented to and not excluded by the court, the motion must be treated as one for summary judgment under Rule 56. All parties must be given a reasonable opportunity to present all the material that is pertinent to the motion.
(e) Motion for a More Definite Statement. A party may move for a more definite statement of a pleading to which a responsive pleading is allowed but which is so vague or ambiguous that the party cannot reasonably prepare a response. The motion must be made before filing a responsive pleading and must point out the defects complained of and the details desired. if the court orders a more definite statement and the order is not obeyed within 14 days after notice of the order or within the time the court sets, the court may strike the pleading or issue any other appropriate order.

(f) Motion to Strike. The court may strike from a pleading an insufficient defense or any redundant, immaterial, impertinent, or scandalous matter. The court may act:
(1) on its own; or
(2) on motion made by a party either before responding to the pleading or, if a response is not allowed, within 21 days after being served with the pleading.
(g) Joining Motions.
(1) Right to Join. A motion under this rule may be joined with any other motion allowed by this rule.
(2) Limitation on Further Motions. Except as provided in Rule 12(h)(2) or (3), a party that makes a motion under this rule must not make another motion under this rule raising a defense or objection that was available to the party but omitted from its earlier motion.

(h) Waiving and Preserving Certain Defenses.
(1) When Some Are Waived. A party waives any defense listed in Rule 12(b)(2)-(5) by:
(A) omitting it from a motion in the circumstances described in Rule 12(g)(2); or
(B) failing to either:
(i) make it by motion under this rule; or
(ii) include it in a responsive pleading or in an amendment allowed by Rule 15(a)(1) as a matter of course.
(2) When to Raise Others. Failure to state a claim upon which relief can be granted, to join a person required by Rule 19(b), or to state a legal defense to a claim may be raised:
(A) in any pleading allowed or ordered under Rule 7(a);
(B) by a motion under Rule 12(c); or
(c) at trial.
(3) Lack of Subject-Matter Jurisdiction. If the court determines at any time that it lacks subject-matter jurisdiction, the court must dismiss the action.
(i) Hearing Before Trial. If a party so moves, any defense listed in Rule 12(b)(1)-(7)一whether made in a pleading or by motion一 and a motion under Rule 12(c) must be heard and decided before trial unless the court orders a deferral until trial.
(As amended Dec. 27, 1946, eff. Mar. 19, 1948; Jan. 21, 1963, eff. July 1, 1963; Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 22, 1993, eff. Dec. 1, 1993; Apr. 17, 2000, eff. Dec. 1, 2000; Apr. 30, 2007, eff. Dec. 1, 2007; Mar. 26, 2009, eff. Dec. 1, 2009.)

Rule 13. Counterclaim and Crossclaim
(a) Compulsory Counterclaim.
(1) In General. A pleading must state as a counterclaim any claim that一at the time of its service一the pleader has against an opposing party if the claim:
(A) arises out of the transaction or occurrence that is the subject matter of the opposing party's claim; and
(B) does not require adding another party over whom the court cannot acquire jurisdiction.
(2) Exceptions. The pleader need not state the claim if:
(A) when the action was commenced, the claim was the subject of another pending action; or
(B) the opposing party sued on its claim by attachment or other process that did not establish personal jurisdiction over the pleader on that claim, and the pleader does not assert any counterclaim under this rule.

(b) Permissive Counterclaim. A pleading may state as a counterclaim against an opposing party any claim that is not compulsory.
(c) Relief Sought in a Counterclaim. A counterclaim need not diminish or defeat the recovery sought by the opposing party. It may request relief that exceeds in amount or differs in kind from the relief sought by the opposing party.
(d) Counterclaim Against the United States. These rules do not expand the right to assert a counterclaim一or to claim a credit一against the United States or a United States officer or agency.
(e) Counterclaim Maturing or Acquired After Pleading. The court may permit a party to file a supplemental pleading asserting a counterclaim that matured or was acquired by the party after serving an earlier pleading.
(f) [Abrogated.]

(g) Crossclaim Against a Coparty. A pleading may state as a crossclaim any claim by one party against a coparty if the claim arises out of the transaction or occurrence that is the subject matter of the original action or of a counterclaim, or if the claim relates to any property that is the subject matter of the original action. The crossclaim may include a claim that the coparty is or may be liable to the crossclaimant for all or part of a claim asserted in the action against the crossclaimant.
(h) Joining Additional Parties. Rules 19 and 20 govern the addition of a person as a party to a counterclaim or crossclaim.
(i) Separate Trials; Separate Judgments. If the court orders separate trials under Rule 42(b), it may enter judgment on a counterclaim or crossclaim under Rule 54(b) when it has jurisdiction to do so, even if the opposing party's claims have been dismissed or otherwise resolved.
(As amended Dec. 27, 1946, eff. Mar. 19, 1948; Jan. 21, 1963, eff. July 1, 1963; Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 2007, eff. Dec. 1, 2007; Mar. 26, 2009, eff. Dec. 1, 2009.)

Rule 14. Third-Party Practice
(a) When a Defending Party May Bring in a Third Party.
(1) Timing of the Summons and Complaint. A defending party may, as third-party plaintiff, serve a summons and complaint on a nonparty who is or may be liable to it for all or part of the claim against it. But the third-party plaintiff must, by motion, obtain the court's leave if it files the third-party complaint more than 14 days after serving its original answer.
(2) Third-Party Defendant's Claims and Defenses. The person served with the summons and third-party complaint一the (‘third-party defendant'':
(A) must assert any defense against the third-party plaintiff's claim under Rule 12;
(B) must assert any counterclaim against the third-party plaintiff under Rule 13(a), and may assert any counterclaim against the third-party plaintiff under Rule 13(b) or any crossclaim against another third-party defendant under Rule 13(g);
(C) may assert against the plaintiff any defense that the third-party plaintiff has to the plaintiff's claim; and
(D) may also assert against the plaintiff any claim arising out of the transaction or occurrence that is the subject matter of the plaintiff's claim against the third-party plaintiff.
(3) Plaintiff's Claims Against a Third-Party Defendant. The plaintiff may assert against the third-party defendant any claim arising out of the transaction or occurrence that is the subject matter of the plaintiff's claim against the third-party plaintiff. The third-party defendant must then assert any defense under Rule 12 and any counterclaim under Rule 13(a), and may assert any counterclaim under Rule 13(b) or any crossclaim under Rule 13(g).
(4) Motion to Strike, Sever, or Try Separately. Any party may move to strike the third-party claim, to sever it, or to try it separately.
(5) Third-Party Defendant's Claim Against a Nonparty. A third-party defendant may proceed under this rule against a nonparty who is or may be liable to the third-party defendant for all or part of any claim against it.
(6) Third-Party Complaint In Rem. If it is within the admiralty or maritime jurisdiction, a third-party complaint may be in rem. In that event, a reference in this rule to the ‘‘summons'' includes the warrant of arrest, and a reference to the defendant or third-party plaintiff includes, when appropriate, a person who asserts a right under Supplemental Rule C(6)(a)(i) in the property arrested.

(b) When a Plaintiff May Bring in a Third Party. When a claim is asserted against a plaintiff, the plaintiff may bring in a third party if this rule would allow a defendant to do so.
(c) Admiralty or Maritime Claim.
(1) Scope of Impleader. If a plaintiff asserts an admiralty or maritime claim under Rule 9(h), the defendant or a person who asserts a right under Supplemental Rule C(6)(a)(i) may, as a third-party plaintiff, bring in a third-party defendant who may be wholly or partly liable一either to the plaintiff or to the third-party plaintiff一for remedy over, contribution, or otherwise on account of the same transaction, occurrence, or series of transactions or occurrences.
(2) Defending Against a Demand for Judgment for the Plaintiff. The third-party plaintiff may demand judgment in the plaintiff's favor against the third-party defendant. in that event, the third-party defendant must defend under Rule 12 against the plaintiff's claim as well as the third-party plaintiff's claim; and the action proceeds as if the plaintiff had sued both the third-party defendant and the third-party plaintiff.
(As amended Dec. 27, 1946, eff. Mar. 19, 1948; Jan. 21, 1963, eff. July 1, 1963; Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 17, 2000, eff. Dec. 1, 2000; Apr. 12, 2006, eff. Dec. 1, 2006; Apr. 30, 2007, eff. Dec. 1, 2007; Mar. 26, 2009, eff. Dec. 1, 2009.)

Rule 15. Amended and Supplemental Pleadings
(a) Amendments Before Trial.
(1) Amending as a Matter of Course. A party may amend its pleading once as a matter of course no later than:
(A) 21 days after serving it, or
(b) if the pleading is one to which a responsive pleading is required, 21 days after service of a responsive pleading or 21 days after service of a motion under Rule 12(b), (e), or (f), whichever is earlier.
(2) Other Amendments. In all other cases, a party may amend its pleading only with the opposing party's written consent or the court's leave. The court should freely give leave when justice so requires.
(3) Time to Respond. Unless the court orders otherwise, any required response to an amended pleading must be made within the time remaining to respond to the original pleading or within 14 days after service of the amended pleading, whichever is later.

(b) Amendments During and After Trial.
(1) Based on an Objection at Trial. If, at trial, a party objects that evidence is not within the issues raised in the pleadings, the court may permit the pleadings to be amended. The court should freely permit an amendment when doing so will aid in presenting the merits and the objecting party fails to satisfy the court that the evidence would prejudice that party's action or defense on the merits. The court may grant a continuance to enable the objecting party to meet the evidence.
(2) For Issues Tried by Consent. When an issue not raised by the pleadings is tried by the parties' express or implied consent, it must be treated in all respects as if raised in the pleadings. A party may move一at any time, even after judgment一 to amend the pleadings to conform them to the evidence and to raise an unpleaded issue. But failure to amend does not affect the result of the trial of that issue.

(c) Relation Back of Amendments.
(1) When an Amendment Relates Back. An amendment to a pleading relates back to the date of the original pleading when:
(A) the law that provides the applicable statute of limitations allows relation back;
(B) the amendment asserts a claim or defense that arose out of the conduct, transaction, or occurrence set out一or attempted to be set out一in the original pleading; or
(C) the amendment changes the party or the naming of the party against whom a claim is asserted, if Rule 15(c)(1)(B) is satisfied and if, within the period provided by Rule 4(m) for serving the summons and complaint, the party to be brought in by amendment:
(i) received such notice of the action that it will not be prejudiced in defending on the merits; and
(ii) knew or should have known that the action would have been brought against it, but for a mistake concerning the proper party's identity.
(2) Notice to the United States. When the United States or a United states officer or agency is added as a defendant by amendment, the notice requirements of Rule 15(c)(1)(C)(i) and (ii) are satisfied if, during the stated period, process was delivered or mailed to the United States attorney or the United States attorney's designee, to the Attorney General of the United States, or to the officer or agency.

(d) Supplemental Pleadings. On motion and reasonable notice, the court may, on just terms, permit a party to serve a supplemental pleading setting out any transaction, occurrence, or event that happened after the date of the pleading to be supplemented. The court may permit supplementation even though the original pleading is defective in stating a claim or defense. The court may order that the opposing party plead to the supplemental pleading within a specified time.
(As amended Jan. 21, 1963, eff. July 1, 1963; Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 1991, eff. Dec. 1, 1991; Pub. L. 102-198, §11(a), Dec. 9, 1991, 105 Stat. 1626; Apr. 22, 1993, eff. Dec. 1, 1993; Apr. 30, 2007, eff. Dec. 1, 2007; Mar. 26, 2009, eff. Dec. 1, 2009; Apr. 24, 2023, eff. Dec. 1, 2023.)

Rule 16. Pretrial Conferences; Scheduling; Management
(a) Purposes of a Pretrial Conference. In any action, the court may order the attorneys and any unrepresented parties to appear for one or more pretrial conferences for such purposes as:
(1) expediting disposition of the action;
(2) establishing early and continuing control so that the case will not be protracted because of lack of management;
(3) discouraging wasteful pretrial activities;
(4) improving the quality of the trial through more thorough preparation; and
(5) facilitating settlement.

(b) Scheduling.
(1) Scheduling Order. Except in categories of actions exempted by local rule, the district judge一or a magistrate judge when authorized by local rule一must issue a scheduling order:
(A) after receiving the parties' report under Rule 26(f); or
(B) after consulting with the parties' attorneys and any unrepresented parties at a scheduling conference.
(2) Time to Issue. The judge must issue the scheduling order as soon as practicable, but unless the judge finds good cause for delay, the judge must issue it within the earlier of 90 days after any defendant has been served with the complaint or 60 days after any defendant has appeared.
(3) Contents of the Order.
(A) Required Contents. The scheduling order must limit the time to join other parties, amend the pleadings, complete discovery, and file motions.
(B) Permitted Contents. The scheduling order may:
(i) modify the timing of disclosures under Rules 26(a) and 26(e)(1);
(ii) modify the extent of discovery;
(iii) provide for disclosure, discovery, or preservation of electronically stored information;
(iv) include any agreements the parties reach for asserting claims of privilege or of protection as trialpreparation material after information is produced, including agreements reached under Federal Rule of Evidence 502;
(v) direct that before moving for an order relating to discovery, the movant must request a conference with the court;
(vi) set dates for pretrial conferences and for trial; and
(vii) include other appropriate matters.
(4) Modifying a Schedule. A schedule may be modified only for good cause and with the judge's consent.

(c) Attendance and Matters for Consideration at a Pretrial Conference.
(1) Attendance. A represented party must authorize at least one of its attorneys to make stipulations and admissions about all matters that can reasonably be anticipated for discussion at a pretrial conference. If appropriate, the court may require that a party or its representative be present or reasonably available by other means to consider possible settlement.
(2) Matters for Consideration. At any pretrial conference, the court may consider and take appropriate action on the following matters:
(A) formulating and simplifying the issues, and eliminating frivolous claims or defenses;
(B) amending the pleadings if necessary or desirable;
(C) obtaining admissions and stipulations about facts and documents to avoid unnecessary proof, and ruling in advance on the admissibility of evidence;
(D) avoiding unnecessary proof and cumulative evidence, and limiting the use of testimony under Federal Rule of Evidence 702;
(E) determining the appropriateness and timing of summary adjudication under Rule 56;
(F) controlling and scheduling discovery, including orders affecting disclosures and discovery under Rule 26 and Rules 29 through 37;
(G) identifying witnesses and documents, scheduling the filing and exchange of any pretrial briefs, and setting dates for further conferences and for trial;
(H) referring matters to a magistrate judge or a master;
(I) settling the case and using special procedures to assist in resolving the dispute when authorized by statute or local rule;
(J) determining the form and content of the pretrial order;
(K) disposing of pending motions;
(L) adopting special procedures for managing potentially difficult or protracted actions that may involve complex issues, multiple parties, difficult legal questions, or unusual proof problems;
(M) ordering a separate trial under Rule 42(b) of a claim, counterclaim, crossclaim, third-party claim, or particular issue;
(N) ordering the presentation of evidence early in the trial on a manageable issue that might, on the evidence, be the basis for a judgment as a matter of law under Rule 50(a) or a judgment on partial findings under Rule 52(c);
(O) establishing a reasonable limit on the time allowed to present evidence; and
(P) facilitating in other ways the just, speedy, and inexpensive disposition of the action.

(d) Pretrial Orders. After any conference under this rule, the court should issue an order reciting the action taken. This order controls the course of the action unless the court modifies it.
(e) Final Pretrial Conference and Orders. The court may hold a final pretrial conference to formulate a trial plan, including a plan to facilitate the admission of evidence. The conference must be held as close to the start of trial as is reasonable, and must be attended by at least one attorney who will conduct the trial for each party and by any unrepresented party. The court may modify the order issued after a final pretrial conference only to prevent manifest injustice.
(f) Sanctions.
(1) In General. On motion or on its own, the court may issue any just orders, including those authorized by Rule 37(b)(2)(A)(ii)-(vii), if a party or its attorney:
(A) fails to appear at a scheduling or other pretrial conference;
(B) is substantially unprepared to participate一or does not participate in good faith一in the conference; or
(C) fails to obey a scheduling or other pretrial order.
(2) Imposing Fees and Costs. Instead of or in addition to any other sanction, the court must order the party, its attorney, or both to pay the reasonable expenses一including attorney's fees一incurred because of any noncompliance with this rule, unless the noncompliance was substantially justified or other circumstances make an award of expenses unjust.
(As amended Apr. 28, 1983, eff. Aug. 1, 1983; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 22, 1993, eff. Dec. 1, 1993; Apr. 12, 2006, eff. Dec. 1, 2006; Apr. 30, 2007, eff. Dec. 1, 2007; Apr. 29, 2015, eff. Dec. 1, 2015.)

TITLE IV. PARTIES
Rule 17. Plaintiff and Defendant; Capacity; Public Officers
(a) Real Party in Interest.
(1) Designation in General. An action must be prosecuted in the name of the real party in interest. The following may sue in their own names without joining the person for whose benefit the action is brought:
(A) an executor;
(B) an administrator;
(c) a guardian;
(D) a bailee;
(E) a trustee of an express trust;
(F) a party with whom or in whose name a contract has been made for another's benefit; and
(G) a party authorized by statute.
(2) Action in the Name of the United States for Another's Use or Benefit. When a federal statute so provides, an action for another's use or benefit must be brought in the name of the United States.
(3) Joinder of the Real Party in Interest. The court may not dismiss an action for failure to prosecute in the name of the real party in interest until, after an objection, a reasonable time has been allowed for the real party in interest to ratify, join, or be substituted into the action. After ratification, joinder, or substitution, the action proceeds as if it had been originally commenced by the real party in interest.

(b) Capacity to Sue or Be Sued. Capacity to sue or be sued is determined as follows:
(1) for an individual who is not acting in a representative capacity, by the law of the individual's domicile;
(2) for a corporation, by the law under which it was organized; and
(3) for all other parties, by the law of the state where the court is located, except that:
(A) a partnership or other unincorporated association with no such capacity under that state's law may sue or be sued in its common name to enforce a substantive right existing under the United States Constitution or laws; and
(B) 28 U.S.C. §§754 and 959(a) govern the capacity of a receiver appointed by a United States court to sue or be sued in a United States court.

(c) Minor or Incompetent Person.
(1) With a Representative. The following representatives may sue or defend on behalf of a minor or an incompetent person:
(A) a general guardian;
(B) a committee;
(c)a conservator; or
(D) a like fiduciary.
(2) Without a Representative. A minor or an incompetent person who does not have a duly appointed representative may sue by a next friend or by a guardian ad litem. The court must appoint a guardian ad litem一or issue another appropriate order一to protect a minor or incompetent person who is unrepresented in an action.

(d) Public Officer's Title and Name. A public officer who sues or is sued in an official capacity may be designated by official title rather than by name, but the court may order that the officer's name be added.
(As amended Dec. 27, 1946, eff. Mar. 19, 1948; Dec. 29, 1948, eff. Oct. 20, 1949; Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 25, 1988, eff. Aug. 1, 1988; Pub. L. 100-690, title VII, §7049, Nov.
18, 1988, 102 Stat. 4401; Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 18. Joinder of Claims
(a) In General. A party asserting a claim, counterclaim, crossclaim, or third-party claim may join, as independent or alternative claims, as many claims as it has against an opposing party.
(b) Joinder of Contingent Claims. A party may join two claims even though one of them is contingent on the disposition of the other; but the court may grant relief only in accordance with the parties' relative substantive rights. in particular, a plaintiff may state a claim for money and a claim to set aside a conveyance that is fraudulent as to that plaintiff, without first obtaining a judgment for the money.
(As amended Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 19. Required Joinder of Parties
(a) Persons Required to Be Joined if Feasible.
(1) Required Party. A person who is subject to service of process and whose joinder will not deprive the court of subjectmatter jurisdiction must be joined as a party if:
(A) in that person's absence, the court cannot accord complete relief among existing parties; or
(B) that person claims an interest relating to the subject of the action and is so situated that disposing of the action in the person's absence may:
(i) as a practical matter impair or impede the person's ability to protect the interest; or
(ii) leave an existing party subject to a substantial risk of incurring double, multiple, or otherwise inconsistent obligations because of the interest.
(2) Joinder by Court Order. If a person has not been joined as required, the court must order that the person be made a party. A person who refuses to join as a plaintiff may be made either a defendant or, in a proper case, an involuntary plaintiff.
(3) Venue. If a joined party objects to venue and the joinder would make venue improper, the court must dismiss that party.

(b) When Joinder Is Not Feasible. If a person who is required to be joined if feasible cannot be joined, the court must determine whether, in equity and good conscience, the action should proceed among the existing parties or should be dismissed. The factors for the court to consider include:
(1) the extent to which a judgment rendered in the person's absence might prejudice that person or the existing parties;
(2) the extent to which any prejudice could be lessened or avoided by:
(A) protective provisions in the judgment;
(B) shaping the relief; or
(C) other measures;
(3) whether a judgment rendered in the person's absence would be adequate; and
(4) whether the plaintiff would have an adequate remedy if the action were dismissed for nonjoinder.

(c) Pleading the Reasons for Nonjoinder. When asserting a claim for relief, a party must state:
(1) the name, if known, of any person who is required to be joined if feasible but is not joined; and
(2) the reasons for not joining that person.
(d) Exception for Class Actions. This rule is subject to Rule 23.
(As amended Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 20. Permissive Joinder of Parties
(a) Persons Who May Join or Be Joined.
(1) Plaintiffs. Persons may join in one action as plaintiffs if:
(A) they assert any right to relief jointly, severally, or in the alternative with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences; and
(B) any question of law or fact common to all plaintiffs will arise in the action.
(2) Defendants. Persons—as well as a vessel, cargo, or other property subject to admiralty process in rem一may be joined in one action as defendants if:
(A) any right to relief is asserted against them jointly, severally, or in the alternative with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences; and
(B) any question of law or fact common to all defendants will arise in the action.
(3) Extent of Relief. Neither a plaintiff nor a defendant need be interested in obtaining or defending against all the relief demanded. The court may grant judgment to one or more plaintiffs according to their rights, and against one or more defendants according to their liabilities.
(b) Protective Measures. The court may issue orders一includ-ing an order for separate trials—to protect a party against embarrassment, delay, expense, or other prejudice that arises from including a person against whom the party asserts no claim and who asserts no claim against the party.
(As amended Feb. 28, 1966, eff. July 1, 1966; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 21. Misjoinder and Nonjoinder of Parties
Misjoinder of parties is not a ground for dismissing an action. On motion or on its own, the court may at any time, on just terms, add or drop a party. The court may also sever any claim against a party.
(As amended Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 22. Interpleader
(a) Grounds.
(1) By a Plaintiff. Persons with claims that may expose a plaintiff to double or multiple liability may be joined as defendants and required to interplead. Joinder for interpleader is proper even though:
(A) the claims of the several claimants, or the titles on which their claims depend, lack a common origin or are adverse and independent rather than identical; or
(B) the plaintiff denies liability in whole or in part to any or all of the claimants.
(2) By a Defendant. A defendant exposed to similar liability may seek interpleader through a crossclaim or counterclaim.
(b) Relation to Other Rules and Statutes. This rule supplements一and does not limit—the joinder of parties allowed by Rule 20. The remedy this rule provides is in addition to一and does not supersede or limit—the remedy provided by 28 U.S.C. §§1335, 1397, and 2361. An action under those statutes must be conducted under these rules.
(As amended Dec. 29, 1948, eff. Oct. 20, 1949; Mar. 2, 1987, eff. Aug. 1, 1987; Apr. 30, 2007, eff. Dec. 1, 2007.)

Rule 23. Class Actions
(a) Prerequisites. One or more members of a class may sue or be sued as representative parties on behalf of all members only if:
(1) the class is so numerous that joinder of all members is impracticable;
(2) there are questions of law or fact common to the class;
(3) the claims or defenses of the representative parties are typical of the claims or defenses of the class; and
(4) the representative parties will fairly and adequately protect the interests of the class.

(b) Types of Class Actions. A class action may be maintained if Rule 23(a) is satisfied and if:
(1) prosecuting separate actions by or against individual class members would create a risk of:
(A) inconsistent or varying adjudications with respect to individual class members that would establish incompatible standards of conduct for the party opposing the class; or
(B) adjudications with respect to individual class members that, as a practical matter, would be dispositive of the interests of the other members not parties to the individual adjudications or would substantially impair or impede their ability to protect their interests;
(2) the party opposing the class has acted or refused to act on grounds that apply generally to the class, so that final injunctive relief or corresponding declaratory relief is appropriate respecting the class as a whole; or
(3) the court finds that the questions of law or fact common to class members predominate over any questions affecting only individual members, and that a class action is superior to other available methods for fairly and efficiently adjudicating the controversy. The matters pertinent to these findings include:
(A) the class members' interests in individually controlling the prosecution or defense of separate actions;
(B) the extent and nature of any litigation concerning the controversy already begun by or against class members;
(C) the desirability or undesirability of concentrating the litigation of the claims in the particular forum; and
(D) the likely difficulties in managing a class action.

(c) Certification Order; Notice to Class Members; Judgment; Issues Classes; Subclasses.
(1) Certification Order.
(A) Time to Issue. At an early practicable time after a person sues or is sued as a class representative, the court must determine by order whether to certify the action as a class action.
(B) Defining the Class; Appointing Class Counsel. An order that certifies a class action must define the class and the class claims, issues, or defenses, and must appoint class counsel under Rule 23(g).
(C) Altering or Amending the Order. An order that grants or denies class certification may be altered or amended before final judgment.