Rule 55.01.Pleading Required.

Rule 55.01 lays out the closed set of pleadings a Missouri civil case runs on. Every case needs a petition and an answer. If the answer contains a counterclaim, the plaintiff must file a reply to it. If a defendant’s answer contains a cross-claim against a co-defendant, that co-defendant must answer it. And when a party brings in someone new under the third-party practice rule, a third-party petition and a third-party answer join the file.

The rule also flags a particular defense that must be pleaded instead of left implicit: an “affirmative avoidance.” That’s a defense that doesn’t just deny the plaintiff’s facts but adds new matter — something like a release, a waiver, or a statute of limitations bar — that would defeat the claim even if the plaintiff’s version of events is true. Because this new matter shows up in the answer, the plaintiff needs the chance to respond to it, which is part of why a reply exists as a recognized pleading.

Beyond that closed list, the rule shuts the door on extra pleadings. No surreply, no rejoinder, no additional round of paper unless a judge specifically orders one. That keeps the pleading stage from sprawling into an open-ended exchange and pushes disputes toward motions and discovery instead.