Joinder of Claims (Rule 18) vs. Joinder of Parties (Rule 20)
A detailed comparison of these two civil procedure rules, including key differences, exam strategies, and guidance on when to apply each.
Overview
Rule 18 (joinder of claims) and Rule 20 (joinder of parties) are both joinder provisions in the Federal Rules of Civil Procedure, but they address different aspects of structuring a lawsuit. Rule 18 governs how many claims a party can assert, while Rule 20 governs who can be joined as a party.
Rule 18(a) is permissive and extremely broad: once a party has a claim against another party, they may join as many additional claims as they have, regardless of whether the claims are related. There is no requirement that the claims arise from the same transaction or share common questions. The practical limitation on Rule 18 is subject matter jurisdiction: each claim must have an independent basis for federal jurisdiction or qualify for supplemental jurisdiction under 28 U.S.C. Section 1367.
Rule 20(a) is also permissive but imposes substantive requirements. Persons may be joined as plaintiffs or defendants only if: (1) their claims or the claims against them arise out of the same transaction, occurrence, or series of transactions or occurrences, and (2) there is a common question of law or fact. Both requirements must be satisfied. Rule 20 prevents unrelated parties from being lumped together in a single lawsuit merely for convenience.
The two rules interact in an important way. Rule 20 determines who can be in the lawsuit; once a party is properly joined under Rule 20, Rule 18 permits them to assert any and all claims they have against other parties. So the transaction-or-occurrence and common-question requirements in Rule 20 function as a gateway, and Rule 18 opens the floodgates for additional claims once the party is through the gate.
Key Differences
| Aspect | Joinder of Claims (Rule 18) | Joinder of Parties (Rule 20) |
|---|---|---|
| What it governs | Number and type of claims a party can bring | Who can be joined as parties to the action |
| Requirements | None; any claims may be joined once a party has one valid claim | Same transaction/occurrence AND common question of law or fact |
| Mandatory or permissive | Permissive (party may join claims but is not required to) | Permissive (parties may be joined but are not required to be) |
| Jurisdictional limitation | Each claim needs independent jurisdiction or supplemental jurisdiction | Each party's claims need independent jurisdiction (supplemental jurisdiction may apply) |
| Relationship between claims/parties | Claims need not be related at all | Claims must arise from same transaction and share common questions |
Exam Tips
On a civil procedure exam, analyze Rule 20 before Rule 18. First determine whether the parties are properly joined (same transaction/occurrence plus common question). Once parties are properly in the case, Rule 18 allows them to add any claims they wish. A common exam trap involves a plaintiff trying to join an unrelated defendant: Rule 20 prevents this even though Rule 18 would allow unrelated claims against an already-joined defendant. Always address subject matter jurisdiction for each claim, as supplemental jurisdiction under Section 1367 may or may not be available depending on whether the claims share a common nucleus of operative fact.
When to Apply Which
Apply Rule 20 when the question is whether additional parties can be brought into the lawsuit. Apply Rule 18 when the question is whether a party already in the lawsuit can assert additional claims. The order of analysis matters: determine proper parties first (Rule 20), then address the scope of claims each party can bring (Rule 18). Remember that even though Rule 18 has no relatedness requirement, subject matter jurisdiction imposes a practical limit on unrelated claims.