A defendant ordinarily responds to a plaintiff’s complaint by filing an answer under Federal Rule of Civil Procedure 12(a). In certain circumstances, however, the Federal Rules permit a defendant to assert preliminary defenses by motion before answering. In those cases, a defendant may file a motion to dismiss under Federal Rule of Civil Procedure 12(b), which lists the defenses that may be raised by pre-answer motion.
As a general rule, defenses asserted under Rule 12(b) must be raised before the defendant serves a responsive pleading, if a responsive pleading is required. Fed. R. Civ. P. 12(b). When a responsive pleading is required, the deadline to file a Rule 12(b) motion typically corresponds to the deadline for serving an answer under Rule 12(a), which is generally 21 days after service of the operative complaint, unless a different deadline applies (for example, where service is waived).
Certain Rule 12(b) defenses—lack of personal jurisdiction, improper venue, insufficient process, and insufficient service of process—are waived if not raised in the defendant’s first Rule 12 motion or responsive pleading. Fed. R. Civ. P. 12(h)(1). Other defenses, including failure to state a claim upon which relief can be granted and failure to join a required party, may be raised later in the case, including in a motion for judgment on the pleadings under Rule 12(c) or at trial. Fed. R. Civ. P. 12(h)(2). A challenge to subject-matter jurisdiction may be raised at any time. Fed. R. Civ. P. 12(h)(3).
Rule 12(b) motions are often referred to as “pre-answer motions” because they are commonly filed at the outset of a case. A successful Rule 12(b) motion may eliminate the need for the defendant to file an answer altogether, which can provide a significant tactical advantage. For example, if the court lacks subject-matter jurisdiction over the claims asserted in the complaint, the court has no authority to adjudicate the dispute. In that circumstance, there is no reason for a defendant to plead defenses to an action that cannot be maintained in federal court.
Similar threshold defenses exist where the court lacks personal jurisdiction over the defendant or where venue is improper. Other Rule 12(b) defenses focus on defects in the manner in which the plaintiff initiated the action. Insufficient process and insufficient service of process challenge whether the summons and complaint were properly issued or served, while a motion based on failure to join a required party attacks the scope of the plaintiff’s suit.
A motion under Rule 12(b)(6), which replaced the common-law demurrer, challenges the legal sufficiency of the complaint. A defendant moving for dismissal under Rule 12(b)(6) asserts that the plaintiff has “failed to state a claim upon which relief can be granted,” meaning that even if all well-pleaded factual allegations are accepted as true, the plaintiff is not entitled to relief as a matter of law. For example, if a plaintiff brings a defamation claim in a jurisdiction that requires publication of the allegedly defamatory statement as an element of the claim, and the complaint fails to allege publication, dismissal under Rule 12(b)(6) may be appropriate.