UBE Joinder of Claims and Parties

Last updated: May 2, 2026

Joinder of Claims and Parties questions are one of the highest-leverage areas to study for the UBE. This guide breaks down the rule, the elements you need to recognize, the named traps that catch most students, and a memory aid that scales to test day. Read it once, then practice the same sub-topic adaptively in the app.

The rule

Under the Federal Rules of Civil Procedure, a party may join any number of claims, and parties may be joined permissively, compulsorily, or via impleader, cross-claim, intervention, or interpleader, subject to subject-matter jurisdiction and venue requirements. Rule 18(a) allows unlimited claim joinder against an opposing party. Rule 20(a) allows permissive party joinder when claims arise from the same transaction or occurrence (T/O) and share a common question of law or fact. Rule 19 compels joinder of certain absent parties whose absence prevents complete relief or threatens existing parties' interests; Rule 14 (impleader), Rule 13 (counter/cross-claims), Rule 24 (intervention), and Rule 22 (interpleader) round out the federal joinder toolkit. Supplemental jurisdiction under 28 U.S.C. § 1367 typically supports joined claims in the same case or controversy, but § 1367(b) carves out plaintiff-side joinder in diversity cases.

Elements breakdown

Joinder of Claims (Rule 18(a))

A party asserting a claim may join, as independent or alternative claims, as many claims as it has against an opposing party.

  • Claimant has at least one proper claim against opposing party
  • Additional claims are against the same opposing party
  • Each joined claim has independent jurisdictional basis or supplemental jurisdiction

Common examples:

  • Plaintiff suing defendant for breach of contract joins unrelated tort claim
  • Defendant asserting counterclaim adds a second unrelated counterclaim

Permissive Party Joinder (Rule 20(a))

Plaintiffs may join, or be joined as defendants, when claims arise from the same transaction or occurrence and share a common question of law or fact.

  • Right to relief asserted jointly, severally, or in alternative
  • Claims arise from same transaction, occurrence, or series of T/O
  • At least one common question of law or fact
  • Court has SMJ, PJ, and venue over each party

Common examples:

  • Multiple passengers from one bus crash sue the bus company
  • Two co-defendants alleged to have jointly defrauded plaintiff

Compulsory Party Joinder (Rule 19)

An absent party must be joined if feasible when its absence prevents complete relief or impairs its interests, and if joinder is infeasible the court decides whether to proceed or dismiss in equity and good conscience.

  • Absent party is 'required' under Rule 19(a) (complete relief unavailable, or absent party's interest impaired, or risk of inconsistent obligations)
  • Joinder is feasible (does not destroy diversity, court has PJ)
  • If infeasible, court applies Rule 19(b) factors to decide whether absentee is 'indispensable'

Common examples:

  • Co-obligee on a contract not joined in suit to enforce
  • Co-owner of disputed property absent from quiet-title action

Counterclaims (Rule 13(a)–(b))

A compulsory counterclaim arises out of the same T/O as the opposing party's claim and is waived if not pleaded; a permissive counterclaim need not arise from the same T/O.

  • Compulsory: arises from same T/O as opposing claim and exists at time of pleading
  • Compulsory: must be pleaded or waived
  • Permissive: any other claim against opposing party may be asserted
  • Permissive counterclaim requires independent jurisdictional basis

Cross-Claims (Rule 13(g))

A party may assert a cross-claim against a coparty if the claim arises out of the same T/O as the original action or a counterclaim, or relates to property at issue.

  • Asserted against a coparty (same side of v.)
  • Arises out of same T/O as the original action or counterclaim
  • Cross-claims are always permissive (never waived if omitted)

Impleader / Third-Party Practice (Rule 14(a))

A defending party may bring in a nonparty who is or may be liable to it for all or part of the original claim, typically on indemnity, contribution, or subrogation theories.

  • Defending party serves third-party complaint as third-party plaintiff
  • Third-party defendant 'is or may be liable' to defending party
  • Liability is derivative of original claim
  • Filed within 14 days of answer or with leave of court

Intervention (Rule 24)

A nonparty may intervene as of right when it has a protectable interest that may be impaired and is not adequately represented; permissive intervention is allowed when the intervenor's claim shares a common question with the action.

  • As of right (24(a)): timely motion
  • As of right: claimed interest in subject of action
  • As of right: disposition may impair or impede that interest
  • As of right: existing parties do not adequately represent intervenor
  • Permissive (24(b)): timely motion and common question of law or fact

Interpleader (Rule 22 and 28 U.S.C. § 1335)

A stakeholder facing multiple adverse claims to a single fund or property may force the claimants to litigate among themselves to avoid double or inconsistent obligations.

  • Stakeholder holds property or money subject to adverse claims
  • Rule 22 (statutory analog): full diversity between stakeholder and at least one claimant; § 1335 requires only minimal diversity among claimants and $500 stake
  • Stakeholder may deposit fund into court registry

Common patterns and traps

The Rule 18 / Rule 20 Switcheroo

The MBE writes a stem that looks like a Rule 20 problem (multiple parties, multiple claims) but is actually a Rule 18 problem because all claims are by one plaintiff against one defendant. Candidates wrongly demand a same-T/O finding when none is needed. Conversely, when there are multiple parties, candidates skip the common-question prong of Rule 20.

A choice that says 'No, because the claims do not arise from the same transaction or occurrence' — correct under Rule 20, but wrong when only Rule 18 is at issue.

The § 1367(b) Diversity Trap

Plaintiffs in a diversity case cannot use supplemental jurisdiction to join claims against parties brought in under Rule 14, 19, 20, or 24 if doing so would violate § 1332's complete-diversity or amount-in-controversy requirement. Defendants face no such bar. Candidates frequently apply § 1367(a) without checking § 1367(b)'s plaintiff-side carve-out.

A choice that says supplemental jurisdiction supports the plaintiff's claim against a non-diverse impleaded third-party defendant — looks right under § 1367(a), but § 1367(b) forbids it.

The Rule 19 'Required' vs 'Indispensable' Conflation

Rule 19(a) labels an absent party 'required.' Only after determining joinder is infeasible does Rule 19(b) ask whether the case can proceed without that party — the 'indispensable' question. Distractors collapse the two steps and dismiss the case the moment a 'required' party can't be joined.

A choice that dismisses immediately after finding the absent party is 'required' under Rule 19(a) without applying the Rule 19(b) equity-and-good-conscience factors.

The Compulsory Counterclaim Waiver

A counterclaim arising from the same transaction or occurrence as the plaintiff's claim is compulsory under Rule 13(a) and is forever waived if omitted. Distractors let the defendant file a separate later action raising what should have been pleaded as a counterclaim.

A choice that allows defendant's later separate suit on a same-T/O claim, ignoring claim-preclusion-style waiver under Rule 13(a).

The Impleader Derivative-Liability Limit

Rule 14(a) only permits impleader on a theory of derivative liability — indemnity, contribution, subrogation. A defendant cannot implead a third party simply because that party may be liable to the plaintiff directly on a separate theory.

A choice that approves impleader where the third party 'may also be liable to the plaintiff on a separate tort' rather than derivatively to the impleading defendant.

How it works

Joinder questions reward a clean two-step: first identify the proper joinder rule, then check jurisdiction. Suppose Reyes (NY) sues Liu Properties, LLC (NY) and Patel Logistics, Inc. (NJ) after a delivery truck owned by Patel collided with Reyes's car at a property managed by Liu. Reyes joins both defendants under Rule 20(a) because the claims arise from the same occurrence (the collision) and share common questions (causation, the property's signage). But because Reyes and Liu are both New Yorkers, the original action lacks complete diversity and there is no federal-question hook — meaning Rule 20 permits joinder, but § 1332 won't support it. Now flip the facts: assume the suit was originally filed under federal-question jurisdiction against Patel only, and Patel impleads Liu under Rule 14(a) for indemnity. Section 1367(a) supplemental jurisdiction supports the impleaded claim because it arises from the same case or controversy, and § 1367(b)'s carve-outs do not bar defendant-initiated joinder. The traps: (1) confusing Rule 18 (claim joinder against the same opposing party — no T/O test) with Rule 20 (party joinder — T/O plus common question), and (2) forgetting that supplemental jurisdiction has different rules for plaintiffs versus defendants in diversity cases.

Worked examples

Worked Example 1

How should the court rule on Liu Industrial's motion to sever?

  • A Grant the motion, because Rule 20 requires that joined claims arise from the same transaction or occurrence.
  • B Grant the motion, because supplemental jurisdiction does not extend to factually unrelated claims under § 1367(a).
  • C Deny the motion, because Rule 18(a) permits a party to join as many claims as it has against an opposing party regardless of factual relationship. ✓ Correct
  • D Deny the motion, but only if the trademark claim independently satisfies federal-question jurisdiction.
  • E

Why C is correct: Rule 18(a) imposes no transaction-or-occurrence limit on the joinder of claims by a single party against the same opposing party. Both claims here are between Reyes and Liu Industrial, are between diverse citizens, and each independently exceeds $75,000 (so § 1332 is satisfied for each). Rule 20 governs joinder of parties — not claims — and is irrelevant when the parties are already properly aligned.

Why each wrong choice fails:

  • A: This applies Rule 20's same-T/O requirement, but Rule 20 governs joinder of parties, not claims. With one plaintiff and one defendant, only Rule 18 controls. (The Rule 18 / Rule 20 Switcheroo)
  • B: Section 1367 supplemental jurisdiction is unnecessary because each claim independently satisfies diversity and amount-in-controversy under § 1332. The choice imports a § 1367(a) limit that is not triggered when each claim has its own jurisdictional basis. (The § 1367(b) Diversity Trap)
  • D: Federal-question jurisdiction is not required because diversity already exists for both claims. Rule 18 has no jurisdictional condition of its own; it only permits joinder if jurisdiction otherwise exists.
Worked Example 2

Should the court dismiss Patel's direct claim against Liu Components?

  • A No, because § 1367(a) supplemental jurisdiction extends to all claims forming part of the same case or controversy.
  • B No, because Liu Components was properly impleaded under Rule 14, and any related claim by the plaintiff against an impleaded party falls within supplemental jurisdiction.
  • C Yes, because Patel's claim against Liu Components fails to satisfy the $75,000 amount-in-controversy requirement.
  • D Yes, because § 1367(b) bars supplemental jurisdiction over plaintiff-asserted claims against persons made parties under Rule 14 when exercising it would be inconsistent with § 1332. ✓ Correct
  • E

Why D is correct: In a diversity case, § 1367(b) carves out plaintiff-side claims against parties joined under Rules 14, 19, 20, or 24 if supplemental jurisdiction would defeat § 1332. Patel and Liu Components are both California citizens (after counting Reyes's California citizenship and Liu's California citizenship — note Patel is Texan, but the carve-out is concerned with whether the claim itself satisfies § 1332's requirements, including amount). Patel's $80,000 claim is below diversity's amount and would also undermine the structure that § 1367(b) exists to protect.

Why each wrong choice fails:

  • A: Section 1367(a) is the starting point, but § 1367(b) overrides it for plaintiff-side joinder in diversity cases. The choice stops at subsection (a) and never reaches the carve-out. (The § 1367(b) Diversity Trap)
  • B: This sounds plausible but is precisely backwards: § 1367(b) specifically singles out claims by plaintiffs against persons made parties under Rule 14 as outside supplemental jurisdiction in diversity cases. (The § 1367(b) Diversity Trap)
  • C: Right outcome, wrong reason. Plaintiffs may aggregate amounts against a single defendant, but the dispositive defect is § 1367(b), not the standalone amount-in-controversy rule. The MBE penalizes correct outcomes paired with wrong rationales.
Worked Example 3

How should the court treat Patel under Rule 19?

  • A Patel must be joined as a required party under Rule 19(a) because complete relief cannot be afforded without him and his interest may be impaired. ✓ Correct
  • B Patel need not be joined because Reyes can seek only her own one-third share, leaving Patel's interest unaffected.
  • C Patel cannot be joined because adding him would destroy complete diversity between Reyes and Liu.
  • D Patel must be joined only if the court finds, after applying the Rule 19(b) factors, that he is indispensable.
  • E

Why A is correct: Rule 19(a) requires joinder when the absent party claims an interest in the subject of the action that disposition may impair, or when complete relief cannot be afforded without the absent party. Patel's co-tenancy interest in the crop proceeds satisfies both tests. Joinder is feasible (Iowa v. Iowa-and-Nebraska still leaves diverse parties on opposite sides if properly aligned, and the court has personal jurisdiction). Because joinder is feasible, the court never reaches Rule 19(b)'s indispensability analysis.

Why each wrong choice fails:

  • B: This ignores that disposing of co-tenancy proceeds in Patel's absence would impair his protectable interest under Rule 19(a)(1)(B). Even if Reyes nominally claims only her share, the judgment will allocate the entire $400,000 crop value.
  • C: The facts state joinder is feasible without destroying jurisdiction. The choice asserts a jurisdictional defect that the question's facts have already foreclosed.
  • D: Rule 19(b)'s 'indispensable' analysis applies only when joinder is infeasible. When joinder is feasible — as here — the court must order it under 19(a) and never reaches 19(b). (The Rule 19 'Required' vs 'Indispensable' Conflation)

Memory aid

'CLAIMS vs PARTIES': Rule 18 joins CLAIMS freely (no T/O); Rule 20 joins PARTIES only if same T/O + common Q. For absent parties, walk Rule 19 in two steps: (a) Required? then (b) Indispensable? — never collapse them.

Key distinction

Rule 18 (claim joinder) has NO transaction-or-occurrence requirement, while Rule 20 (party joinder) requires both same T/O AND a common question of law or fact. The MBE consistently tests this by giving you unrelated claims joined against a single defendant (proper under Rule 18) versus unrelated claims by or against multiple parties (improper under Rule 20).

Summary

Federal joinder is permissive for claims under Rule 18, transactionally limited for parties under Rule 20, and compulsory only when Rule 19's two-step analysis demands it — and every joinder must independently satisfy subject-matter jurisdiction.

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Frequently asked questions

What is joinder of claims and parties on the UBE?

Under the Federal Rules of Civil Procedure, a party may join any number of claims, and parties may be joined permissively, compulsorily, or via impleader, cross-claim, intervention, or interpleader, subject to subject-matter jurisdiction and venue requirements. Rule 18(a) allows unlimited claim joinder against an opposing party. Rule 20(a) allows permissive party joinder when claims arise from the same transaction or occurrence (T/O) and share a common question of law or fact. Rule 19 compels joinder of certain absent parties whose absence prevents complete relief or threatens existing parties' interests; Rule 14 (impleader), Rule 13 (counter/cross-claims), Rule 24 (intervention), and Rule 22 (interpleader) round out the federal joinder toolkit. Supplemental jurisdiction under 28 U.S.C. § 1367 typically supports joined claims in the same case or controversy, but § 1367(b) carves out plaintiff-side joinder in diversity cases.

How do I practice joinder of claims and parties questions?

The fastest way to improve on joinder of claims and parties is targeted, adaptive practice — working questions that focus on your specific weak spots within this sub-topic, getting immediate feedback, and revisiting items you missed on a spaced-repetition schedule. Neureto's adaptive engine does this automatically across the UBE; start a free 7-day trial to see your sub-topic mastery climb in real time.

What's the most important distinction to remember for joinder of claims and parties?

Rule 18 (claim joinder) has NO transaction-or-occurrence requirement, while Rule 20 (party joinder) requires both same T/O AND a common question of law or fact. The MBE consistently tests this by giving you unrelated claims joined against a single defendant (proper under Rule 18) versus unrelated claims by or against multiple parties (improper under Rule 20).

Is there a memory aid for joinder of claims and parties questions?

'CLAIMS vs PARTIES': Rule 18 joins CLAIMS freely (no T/O); Rule 20 joins PARTIES only if same T/O + common Q. For absent parties, walk Rule 19 in two steps: (a) Required? then (b) Indispensable? — never collapse them.

What's a common trap on joinder of claims and parties questions?

Confusing Rule 18 (no T/O required) with Rule 20 (T/O required)

What's a common trap on joinder of claims and parties questions?

Forgetting § 1367(b) bars plaintiff-side joinder in diversity cases

Related UBE sub-topics

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