Joinder of Parties (Rule 20)

Federal Rule of Civil Procedure 20 governs permissive joinder of parties, allowing multiple plaintiffs to join together or multiple defendants to be joined in a single action. The rule has two requirements that must both be satisfied: first, the claims by or against the joined parties must arise out of the same transaction, occurrence, or series of transactions or occurrences; and second, there must be at least one question of law or fact common to all parties sought to be joined.

The transaction or occurrence test under Rule 20 is interpreted broadly to promote trial convenience and judicial economy. Courts look at the logical relationship between the claims and whether they share a substantial factual overlap. The common question requirement is similarly liberal; a single shared question of law or fact suffices. The court retains discretion under Rule 20(b) to order separate trials or make other orders to prevent prejudice or ensure efficiency.

Permissive joinder under Rule 20 must also satisfy subject matter jurisdiction requirements. Each joined party must independently satisfy diversity jurisdiction (including the complete diversity and amount-in-controversy requirements), qualify under federal question jurisdiction, or come within supplemental jurisdiction under section 1367. In diversity cases, section 1367(b) restricts supplemental jurisdiction over claims by plaintiffs joined under Rule 20, preventing plaintiffs from circumventing the complete diversity requirement. After Exxon Mobil Corp. v. Allapattah Services (2005), supplemental jurisdiction may cure a shortfall in the amount in controversy for additional plaintiffs, but it cannot cure a lack of complete diversity.