Joinder
The procedural rules for bringing multiple claims or parties together in a single lawsuit.
The MBE rarely asks “what is joinder”; it tests whether a specific device fits the facts and whether a joined claim still has its own jurisdictional hook. The classic pattern: a party adds a claim or non-diverse party, and the answer turns on supplemental jurisdiction (§ 1367) — note the trap that § 1367(b) bars plaintiffs in a diversity case from using supplemental jurisdiction over parties joined under Rule 14, 19, 20, or 24 when it would defeat complete diversity. Another favorite: a defendant who skips a compulsory counterclaim is barred from raising it in a later suit (after a judgment on the merits); a permissive one survives because it could have been filed separately.
Don’t confuse the cross-claim (against a co-party, Rule 13(g) — must arise from the same transaction) with the counterclaim (against an opposing party). Students also mix up impleader (Rule 14 — a defendant pulls in a third party derivatively liable, “if I’m liable, you owe me”) with interpleader (a stakeholder forces rival claimants to fight over one fund). Hook: co-parties cross, opponents counter.
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