(a) A plaintiff who in a complaint, alone or with coplaintiffs, alleges a cause of action against one or more defendants may unite with such cause any other causes which he has either alone or with any coplaintiffs against any of such defendants.
§ 427.10.Generally
Title 6. Of the Pleadings In Civil Actions · Chapter 2. Pleadings Demanding Relief · Article 3. Permissive Joinder of Causes of Action · Enacted 1971 · no amendments on record · Last verified July 28, 2026
In one sentenceSection 427.10 lets a plaintiff join any number of causes of action against the same defendants in a single complaint, and permits similar joinder of causes of action in a cross-complaint under §§ 428.10 and 428.30.
Full Text of § 427.10
Plain-English Summary
Section 427.10 states California's basic rule of permissive joinder of causes of action. Subdivision (a) lets a plaintiff — alone or together with coplaintiffs — unite any number of causes of action against one or more defendants in a single complaint, so long as the plaintiff (alone or with coplaintiffs) has each of those causes against the defendants named.
Unlike the compulsory cross-complaint rule of § 426.30, this joinder is optional rather than mandatory: a plaintiff is not required to join every available cause of action in one complaint, only permitted to. That flexibility lets a plaintiff bring several distinct claims against the same defendant — say, a contract claim and a separate tort claim arising from unrelated conduct — in one lawsuit rather than filing multiple actions.
Subdivision (b) extends the same logic to cross-complaints by cross-reference: a cross-complainant may join causes of action in a cross-complaint following the rules set out in §§ 428.10 and 428.30, which govern what a cross-complaint may assert and how additional causes may be united with it.
Frequently Asked Questions
Can a plaintiff bring more than one unrelated claim against the same defendant in one lawsuit?
Yes. Section 427.10(a) lets a plaintiff unite any causes of action the plaintiff has against a defendant in a single complaint, regardless of whether those causes are factually related.
Is joining multiple causes of action mandatory?
No. Section 427.10 permits joinder of causes of action; it does not require it. The mandatory rule for related claims against an opposing party comes from § 426.30's compulsory cross-complaint provision instead.
How does joinder work in a cross-complaint?
Section 427.10(b) allows causes of action to be joined in a cross-complaint in accordance with §§ 428.10 and 428.30, which set out what a cross-complaint may include and how additional causes may be added to it.
Amendment History
Added by Stats. 1971, Ch. 244.
Source & verification. Section text is reproduced verbatim from
the Deering's California Codes Annotated / vLex. Enacted by the California Legislature.
Last verified July 28, 2026.
· Official source
Also known as: permissive joinder of causes of action californiajoining multiple claims in one lawsuit california