The party commencing a special proceeding shall be styled the petitioner and any adverse party the respondent. After a proceeding is commenced, no party shall be joined or interpleaded and no third-party practice or intervention shall be allowed, except by leave of court.
§ 401.Parties.
Article 4. Special Proceedings · Last amended 1963 · Last verified July 21, 2026
In one sentenceCPLR 401 names the parties to a special proceeding — the party who starts it is the petitioner and the opposing party is the respondent — and bars adding parties, interpleader, third-party practice, or intervention once the proceeding is underway except by leave of court.
Full Text of CPLR 401
Plain-English Summary
A special proceeding runs on different labels than an ordinary lawsuit. Instead of a plaintiff and a defendant, CPLR 401 gives you a petitioner, the party who commences the case, and a respondent, the party on the other side. The terms track the different paperwork a special proceeding uses — a petition instead of a complaint — but the underlying idea is the same: one side asks the court for relief, and the other side answers.
What sets 401 apart is its second sentence. Once a special proceeding starts, the rule locks the roster of parties in place. No one may join a new party, no one may interplead a stakeholder, and no one may bring in a third party or intervene, unless the court grants leave. Ordinary actions run on far looser joinder rules, letting parties add claims and co-parties as a case develops. Special proceedings trade that flexibility for speed: they exist to get a discrete question decided fast, on papers, without the case sprawling into new fronts.
The leave-of-court exception keeps the rule from becoming absolute. A court that sees a genuine need to bring in another party can still allow it, but the burden sits with the party asking, not with the default rule. Anyone thinking about widening a special proceeding this way should read it together with the petition and answer requirements in CPLR 402, since a new party changes what those pleadings need to say.
Frequently Asked Questions
What's the difference between a petitioner and a plaintiff in New York?
A petitioner is the party who starts a special proceeding, while a plaintiff starts an ordinary action. CPLR 401 uses petitioner and respondent for special proceedings and reserves plaintiff and defendant for actions commenced by a complaint.
Can I add a new party to a special proceeding after I've filed it?
Only with the court's permission. CPLR 401 bars joining or interpleading a party, and bars third-party practice or intervention, once the proceeding has begun, except by leave of court.
What is a special proceeding under New York law?
It's a procedural track, separate from an ordinary action, that CPLR Article 4 governs with its own pleading, notice, and hearing rules. CPLR 401 supplies the party labels — petitioner and respondent — that mark a case as running on this track.
Can someone intervene in a special proceeding without asking the court?
No. CPLR 401 does not allow intervention as of right once the proceeding is commenced; a would-be intervenor needs leave of court first.
Does CPLR 401 allow third-party claims in a special proceeding?
Not without leave of court. The rule groups third-party practice with joinder and intervention as steps that require the court's permission after the proceeding starts.
Advisory Committee Notes
The first sentence of this rule is based upon a similar provision governing actions in the first sentence of CPA § 191. It establishes uniform terminology for the designation of parties in a special proceeding, which avoids the confusing variety of terminology formerly in use and, at the same time, is distinct from that employed in an action. The terms adopted are those used in practice in the greatest number of special proceedings. The petitioner and respondent in a special proceeding correspond to the plaintiff and defendant in an action. Party provisions of article 10 of the new CPLR are intended to be applicable to special proceedings, except that, because a special proceeding is brought before the court immediately, parties may not be added or interpleaded without leave of court, and such leave is also required for third-party practice and intervention. The court in a special proceeding is thus given the degree of control over parties necessary to preserve the summary nature of the proceeding, but it is still able to utilize the party devices of article 10 to prevent an undesirable multiplicity of suits. Requiring a court order in every instance is not unduly burdensome; even if none were required for this purpose, it would almost always be necessary to secure an order extending the time of the hearing or giving the additional party time to plead. It is possible that there will be no adverse party in a special proceeding. See, e. g., CPA art 82 (proceeding for disposition of real property of infant or incompetent). For this reason the term “any adverse party” rather than “the adverse party” is used in the section.
Amendment History
Add, L 1962, ch 308, eff Sept 1, 1963.
Source & verification. Provision text, History, and Advisory
Committee Notes are reproduced verbatim from the Consolidated Laws of New York.
Last verified July 21, 2026.
· Official source
Also known as: petitioner and respondent New Yorkspecial proceeding parties New Yorkjoining parties special proceeding NYCPLR 401 special proceedingsintervention in special proceeding New Yorkthird-party practice special proceeding NY