---
title: "Joinder of Claims (Rule 18)"
type: Legal Rule
source: https://casebriefly.com/legal-rules/joinder-of-claims-rule-18
---

# Joinder of Claims (Rule 18)

Federal Rule 18 permits a party asserting a claim to join as many additional claims as it has against the opposing party, regardless of whether the claims are related, though each claim must independently satisfy subject matter jurisdiction or qualify for supplemental jurisdiction.

## Definition

Federal Rule of Civil Procedure 18 governs the joinder of claims and provides that a party asserting a claim, counterclaim, crossclaim, or third-party claim may join as many claims as it has against an opposing party. Rule 18 is entirely permissive and imposes no requirement of relatedness between claims. A plaintiff suing a defendant for breach of contract may, in the same action, join a claim for personal injury, copyright infringement, or any other claim against that same defendant.

However, Rule 18's permissiveness is subject to an independent jurisdictional requirement. Each claim joined under Rule 18 must have its own basis for subject matter jurisdiction, either through federal question jurisdiction, diversity jurisdiction, or supplemental jurisdiction under 28 U.S.C. section 1367. If a claim shares a common nucleus of operative fact with the anchor claim, supplemental jurisdiction may provide the necessary jurisdictional basis. If it does not, the claim must independently satisfy federal jurisdiction.

Rule 18 operates in conjunction with other joinder rules. For example, once a party has properly joined another party under Rule 20 (permissive joinder of parties), Rule 18 permits the joining party to assert any and all claims it has against the joined party. Similarly, a defendant who has filed a compulsory or permissive counterclaim may join any additional claims against the plaintiff. The practical effect of Rule 18 is to encourage efficient litigation by allowing all disputes between two parties to be resolved in a single proceeding.

## Elements

- A party may join as many claims as it has against the opposing party
- No relatedness requirement between joined claims
- Each claim must independently satisfy subject matter jurisdiction or qualify for supplemental jurisdiction
- Rule 18 is entirely permissive, not mandatory
- Rule 18 works in conjunction with party joinder rules (Rules 13, 14, 20)

## Key Case

United States v. Heyward-Robinson Co., 430 F.2d 1077 (2d Cir. 1970)

## Landmark Cases

| Name | Citation | Significance |
| --- | --- | --- |
| United States v. Heyward-Robinson Co. | 430 F.2d 1077 (2d Cir. 1970) | Addressed the interplay between Rule 18 claim joinder and supplemental jurisdiction, holding that related claims could be heard under ancillary (now supplemental) jurisdiction. |
| Mosley v. General Motors Corp. | 497 F.2d 1330 (8th Cir. 1974) | While primarily a Rule 20 case, illustrates how permissive party joinder interacts with Rule 18 claim joinder in employment discrimination litigation. |
| Harris v. Avery | 5 Kan. 146 (1869) | Early case reflecting the historical common law hostility to claim joinder that the Federal Rules abolished through Rule 18's permissive approach. |

## Exam Tips

- Remember that Rule 18 removes all barriers to claim joinder between existing parties, but does not create subject matter jurisdiction. Always check jurisdiction for each claim separately.
- Rule 18 is permissive, not compulsory. There is no penalty for failing to join a claim under Rule 18, though claim preclusion may bar a party from bringing related claims in a subsequent action.
- On exams, after establishing that parties are properly joined, apply Rule 18 to determine what claims can be asserted between them.

## Common Mistakes

- Assuming that Rule 18 provides an independent basis for subject matter jurisdiction; it does not. Each claim must satisfy jurisdiction independently or through supplemental jurisdiction.
- Confusing Rule 18 (claim joinder, which is purely permissive) with compulsory counterclaim rules under Rule 13(a), which require certain claims to be raised or be forfeited.

## Mnemonic Or Memory Aid

Rule 18 = any claim, any time against the same opposing party. Permissive, unlimited, but jurisdiction still required.

## Related Rules

- joinder-of-parties-rule-20
- supplemental-jurisdiction
- claim-preclusion-res-judicata

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Source: [Joinder of Claims (Rule 18) — CaseBriefly](https://casebriefly.com/legal-rules/joinder-of-claims-rule-18)