Joinder rules trip up more bar takers than you’d expect. Not because they’re complicated in theory, but because the MBE tests them in ways that feel deceptively simple — until you miss the second element.
Permissive joinder under Rule 20 is one of those topics that shows up quietly on the Civil Procedure portion of the MBE and rewards students who actually know the two-part test cold. If you’ve been fuzzy on when multiple parties can or can’t be joined in a single lawsuit, this is your fix.
What Is Permissive Joinder Under Rule 20?
Permissive joinder is the Federal Rule of Civil Procedure that governs when multiple plaintiffs may join together in one lawsuit, or when a plaintiff may sue multiple defendants in a single action. The word “permissive” is important — this rule doesn’t require anyone to join. It simply permits joinder when the conditions are met.
Rule 20 applies to two distinct situations:
- Joinder of plaintiffs — multiple people who want to sue together as co-plaintiffs
- Joinder of defendants — a plaintiff who wants to bring claims against multiple defendants in one action
Both situations are governed by the same two-part test. Know that test, and you know the rule.
The Two-Part Test for Permissive Joinder Under Rule 20
This is the core of what you need. For permissive joinder to be proper under Rule 20, two requirements must both be satisfied:
First: The claims must arise out of the same transaction, occurrence, or series of related transactions or occurrences.
Second: There must be at least one common question of law or fact shared among all the parties being joined.
Both prongs must be met. If either one fails, joinder under Rule 20 is not proper. The MBE will test you on fact patterns where one prong is clearly satisfied but the other quietly isn’t — so read carefully.
Breaking Down the “Same Transaction or Occurrence” Prong
The same transaction or occurrence requirement is broader than it might look. Courts interpret it flexibly. The question is whether there is a logical relationship between the claims — not whether every claim is identical or arose from a single moment in time.
The rule also allows joinder based on a “series of related transactions or occurrences,” which extends the reach further. A pattern of conduct over time can satisfy this prong even if individual incidents happened at different moments.
Here’s a classic MBE-style scenario: Three passengers are injured in a multi-car pileup caused by an allegedly defective traffic signal. All three want to sue the city and the signal manufacturer. The injuries happened in the same accident, arising from the same set of facts. The first prong is clearly satisfied.
Now change the facts slightly: Two plaintiffs were each separately injured by the same defendant’s product, but in unrelated accidents six months apart in different states. That’s a harder call. Courts would look at whether the incidents share enough of a factual nexus to qualify as a “series of related transactions.” If the only link is that the same defendant made the same product, many courts would find the first prong is not met.
Breaking Down the “Common Question” Prong
The common question of law or fact prong is generally the easier one to satisfy. You don’t need every issue to be shared — just one. And that one question can be factual or legal.
Going back to the multi-car pileup: Was the traffic signal defective? That’s a common factual question shared by all three plaintiffs. Prong two is satisfied.
The common question doesn’t need to be the most important issue in the case. It just needs to exist and be genuinely shared. If each plaintiff’s claims turn entirely on individualized facts with no overlap whatsoever, you might have a problem — but that’s a rare scenario when the first prong is already met.
Permissive Joinder of Defendants: Same Test, Different Direction
When a single plaintiff wants to sue multiple defendants in one action, the same two-part test applies. The plaintiff must show that the claims against each defendant arise from the same transaction or occurrence (or series thereof), and that there’s at least one common question of law or fact.
Example: A plaintiff is injured in a construction accident and wants to sue the general contractor, a subcontractor, and the property owner. If the claims all stem from the same worksite accident and share a common question — say, which party was responsible for maintaining the scaffolding — Rule 20 joinder of defendants is proper.
But if the plaintiff tries to sue the general contractor for the worksite accident and a completely unrelated defendant for a car accident that happened the same day, those claims don’t arise from the same transaction or occurrence. No joinder.
The Court’s Discretion to Sever
Even when both Rule 20 prongs are satisfied, joinder isn’t automatic in the sense that courts have discretion to sever claims or order separate trials under FRCP 42(b). If joined claims would cause prejudice, confusion, or undue delay, the court can separate them. This is worth knowing for the MBE — satisfying Rule 20 gets you in the door, but the court can still manage the litigation.
Rule 20 and Subject-Matter Jurisdiction: The Trap You Can’t Miss
Here’s where permissive joinder under Rule 20 intersects with a classic bar exam trap. Satisfying Rule 20 doesn’t automatically solve your jurisdiction problem. Each claim still needs an independent basis for federal subject-matter jurisdiction, or it needs to qualify for supplemental jurisdiction under 28 U.S.C. § 1367.
And here’s the critical wrinkle in diversity cases: supplemental jurisdiction does not extend to claims by plaintiffs against persons made parties under Rule 20 if exercising that jurisdiction would destroy complete diversity. This is explicitly carved out in § 1367(b).
So if you have a diverse plaintiff trying to join a non-diverse defendant under Rule 20 in a diversity case, the court cannot use supplemental jurisdiction to save that claim. The joinder might satisfy Rule 20 on its face, but the court still lacks jurisdiction over that claim. The MBE loves this combination.
Quick Reference: What to Memorize
Before you move on, make sure these are locked in:
- Rule 20 applies to joinder of plaintiffs and joinder of defendants
- Two-part test: (1) same transaction, occurrence, or series of related transactions/occurrences; AND (2) at least one common question of law or fact
- Both prongs must be met — satisfying only one is not enough
- Court discretion: even proper joinder can be severed under FRCP 42(b) to prevent prejudice
- Jurisdiction still matters: in diversity cases, § 1367(b) bars supplemental jurisdiction over Rule 20 parties if it would destroy complete diversity
- “Permissive” means optional — no party is required to join; they are merely permitted to
FlashTables is a set of professionally formatted two-column PDF rule tables covering all seven MBE subjects — 704 rules total, organized by the official NCBE Subject Matter Outline. The Rule 20 permissive joinder test, including its intersection with supplemental jurisdiction under § 1367(b), is laid out side-by-side in the Civil Procedure table alongside the rest of the joinder and jurisdiction rules. Whether you’re a 1L, 2L, or 3L building your civil procedure outline, or a bar taker drilling active recall in the final weeks before the MBE, having these rules in a clean, scannable format means you spend your time learning — not hunting through a casebook.
The Takeaway
Permissive joinder under Rule 20 is a two-prong test. Same transaction or occurrence. Common question of law or fact. Both must be satisfied. Miss one, and joinder isn’t proper. And even when joinder is proper, don’t forget to run the jurisdiction analysis — especially in diversity cases where Rule 20 joinder could blow up complete diversity and § 1367(b) won’t save you.
The MBE doesn’t test whether you vaguely remember Rule 20 exists. It tests whether you can apply both prongs correctly under pressure, and whether you spot the jurisdiction issue hiding underneath. Get those elements cold, and this topic becomes points you don’t give away.