A motion to dismiss is a formal request (usually in a written motion) asking the court to dismiss a lawsuit or case for one of the reasons described in the relevant state or federal rule of civil procedure.

A motion to dismiss is usually filed in the early stages of the litigation and may be required before the party files any other pleading. Some of the common bases on which a case may be dismissed by the court include: (1) statute of limitations expired; (2) lack of subject-matter jurisdiction; (3) lack of personal jurisdiction; (4) improper venue; (5) insufficient process; (6) insufficient service of process; (7) failure to state a claim upon which relief can be granted; and (8) failure to join a party.

In California, a motion to dismiss is typically referred to as a 'demurrer.' Under California law, a demurrer is a pleading used by a defendant to object to a complaint for insufficiency before filing an answer. It is filed early in the litigation process, often before any other pleadings. The grounds for a demurrer in California are similar to those for a motion to dismiss in other jurisdictions and can include the expiration of the statute of limitations, lack of subject-matter jurisdiction, lack of personal jurisdiction, improper venue, and failure to state facts sufficient to constitute a cause of action. If the court sustains the demurrer, the plaintiff may be given an opportunity to amend the complaint to correct the deficiencies. If the plaintiff cannot successfully amend the complaint, the court may dismiss the case. California Code of Civil Procedure sections 430.10 through 430.90 provide the specific grounds and procedures for demurrers.