A Rule 12(b) motion to dismiss is a defendant’s request, made under Federal Rule of Civil Procedure 12(b), to end a lawsuit at the outset on one of seven specific grounds, before any answer is filed and before discovery begins. If a search led you to something called a “112b” motion, that’s the same rule — no procedural code uses “112b,” and the number is almost always a typo for 12(b). A successful motion can end the case on the pleadings alone. An unsuccessful one, or a poorly timed one, can permanently waive defenses the defendant never intended to give up.
The Seven Grounds
Rule 12(b) lists seven defenses a defendant can raise by motion instead of in the answer:1Legal Information Institute. Federal Rules of Civil Procedure Rule 12
- 12(b)(1) — lack of subject matter jurisdiction. The court has no authority over this type of case. Federal courts, for example, generally need a federal question or diversity of citizenship with more than $75,000 at stake.
- 12(b)(2) — lack of personal jurisdiction. The court has no authority over this particular defendant, usually because the defendant lacks minimum contacts with the forum state.
- 12(b)(3) — improper venue. The case was filed in the wrong district under the venue statute.
- 12(b)(4) — insufficient process. The summons document itself is defective, such as a missing signature or wrong court name.
- 12(b)(5) — insufficient service of process. The summons and complaint were delivered in a way the rules don’t allow.
- 12(b)(6) — failure to state a claim upon which relief can be granted. Even accepting every allegation as true, the law provides no remedy.
- 12(b)(7) — failure to join a required party under Rule 19. Someone whose participation the case needs was left out.2Legal Information Institute. Federal Rules of Civil Procedure Rule 19
These grounds do very different things. Some challenge the court’s power. Some challenge how the defendant was notified. One challenges the legal substance of the complaint itself. And they don’t all behave the same way on timing.
Defenses You Lose by Waiting
This is where defendants most often make permanent mistakes. Four of the seven defenses vanish forever if not raised at the first opportunity: 12(b)(2) personal jurisdiction, 12(b)(3) improper venue, 12(b)(4) insufficient process, and 12(b)(5) insufficient service. They must appear in the defendant’s first Rule 12 motion, or, if no motion is filed, in the answer. A defendant who files a 12(b)(6) motion but doesn’t also raise improper venue in that same motion has waived venue for the rest of the case. Rule 12(g)(2) forbids a second Rule 12 motion raising defenses that were available and omitted from the first.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12
Three defenses are treated more generously. Failure to state a claim under 12(b)(6) and failure to join a required party under 12(b)(7) can be raised later, in any pleading, in a motion for judgment on the pleadings, or at trial. Subject matter jurisdiction under 12(b)(1) can be raised at any time by anyone, including the court on its own. A court that discovers mid-trial that it lacks subject matter jurisdiction must dismiss.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12
The practical rule for defense counsel: consolidate every available Rule 12 defense into the first motion, or accept that anything left out of the “waivable four” is gone.
Deadlines and What the Motion Pauses
In federal court, a defendant generally has 21 days after being served with the summons and complaint to file either an answer or a motion to dismiss.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 A defendant who waived formal service under Rule 4(d) gets 60 days from when the waiver request was sent, or 90 days if the defendant is outside the United States. Federal government defendants get 60 days. State court deadlines vary, but 20 to 30 days is common.
Filing the motion pauses the deadline to answer. The defendant does not need to file a responsive pleading until the court rules.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 Discovery is a different story. Filing a motion to dismiss does not automatically stay discovery under the Federal Rules. A defendant who wants discovery halted while the motion is pending has to move separately for a protective order and show good cause.
The motion itself is usually filed with a supporting memorandum of law. Jurisdictional challenges often come with affidavits or declarations — for example, a sworn statement that the defendant has no offices, employees, or business contacts in the forum state. Many federal districts require a meet-and-confer certification confirming that defense counsel contacted the plaintiff’s attorney before filing. Local rules control the details, and they vary meaningfully from district to district.
The 12(b)(6) Standard: Plausibility
The failure-to-state-a-claim motion is the most frequently filed of the seven. It does not dispute the facts the plaintiff alleges. It accepts them as true and asks whether they add up to a legally recognized claim.
For decades, the bar was low: dismissal required showing “beyond doubt” that the plaintiff could prove no set of facts supporting the claim. The Supreme Court raised the standard in 2007 and 2009. A complaint now needs enough factual content to make the claim “plausible on its face.” Labels, legal conclusions, and formulaic recitations of the elements of a cause of action are not enough.
Take a negligence complaint. “The defendant was negligent and I was injured” is a legal conclusion with no facts behind it, and it will not survive. A complaint alleging that the defendant ran a specific red light at a specific intersection and struck the plaintiff’s car, breaking the plaintiff’s leg, gives the court something to evaluate.
On a 12(b)(6) motion, the court generally looks only at the complaint, documents attached to it, documents referenced in it that are central to the claim, and matters of public record subject to judicial notice. If the defendant submits outside evidence and the court considers it, the motion converts into a motion for summary judgment under Rule 56, and both sides get a fair chance to present relevant materials.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12
Responding as the Plaintiff
If you are on the receiving end of a motion to dismiss, the response deadline depends on local rules, but 14 to 21 days from the filing of the motion is typical in federal practice. Missing it can hand the defendant an unopposed dismissal.
A useful opposition brief does two things. It identifies the correct legal standard, and it walks the court through the specific factual allegations that satisfy each element of every claim. Don’t just quote the complaint back. Explain why the allegations, taken as true, make each cause of action plausible. For jurisdictional challenges, put in the facts that establish the court’s authority — the defendant’s contacts with the forum, or the basis for federal question or diversity jurisdiction.
There is also a fallback. If the complaint has fixable problems, ask for leave to amend rather than fighting to defend the current version. Judges commonly grant at least one chance to amend early in a case. Leave is denied when amendment would be futile — when no version of the facts would state a valid claim.
After the Ruling
If the motion is denied, the defendant must file an answer, typically within 14 days of the denial, and the case moves into discovery.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 A denial is not a ruling that the plaintiff will win. It means the complaint clears the threshold to proceed.
If the motion is granted, the decisive question is whether the dismissal is with prejudice or without prejudice. A dismissal without prejudice lets the plaintiff fix the problem and try again: re-serve the defendant properly, file an amended complaint with stronger facts, or refile in a court that has jurisdiction. A dismissal with prejudice is a final judgment on that claim and bars the plaintiff from bringing it again. Courts reserve dismissal with prejudice for situations where no amendment could cure the defect or where the plaintiff has had multiple chances and failed.
A dismissal for lack of subject matter jurisdiction is almost always without prejudice. A court that lacks subject matter jurisdiction never had the power to rule on the merits, so it cannot enter a final merits judgment that blocks a future filing. The plaintiff can refile in a court that does have jurisdiction.
Rule 11 Exposure for Weak Motions
Rule 11 requires that every motion filed with a federal court be supported by a reasonable legal basis. A motion to dismiss built on arguments no competent attorney would advance in good faith can trigger sanctions against the attorney, the firm, or both.3Legal Information Institute. Federal Rules of Civil Procedure Rule 11
Before seeking sanctions, the opposing party must serve the offending side with the sanctions motion and give them 21 days to withdraw or correct the filing. This safe harbor is meant to encourage correction over punishment. If the filing isn’t withdrawn, the court can order non-monetary directives or payment of the opposing party’s attorney’s fees, limited to what is necessary to deter repetition. Courts don’t impose Rule 11 sanctions lightly, but a baseless motion to dismiss is the kind of filing the rule targets.3Legal Information Institute. Federal Rules of Civil Procedure Rule 11