(a) Definition A “complex case” is an action that requires exceptional judicial management to avoid placing unnecessary burdens on the court or the litigants and to expedite the case, keep costs reasonable, and promote effective decision making by the court, the parties, and counsel.
Rule 3.400.Definition
Division 4. Parties and Actions · Last amended 2026 · Last verified July 29, 2026
In one sentenceRule 3.400 defines a 'complex case' as an action needing exceptional judicial management, lists the factors a court weighs in deciding, and names categories of claims — including antitrust, construction defect, securities, mass tort, class action, and groundwater adjudication claims — that are provisionally complex from the start.
Full Text of Rule 3.400
(b) Factors In deciding whether an action is a complex case under (a), the court must consider, among other things, whether the action is likely to involve:
(1) Numerous pretrial motions raising difficult or novel legal issues that will be time- consuming to resolve;
(2) Management of a large number of witnesses or a substantial amount of documentary evidence;
(3) Management of a large number of separately represented parties;
(4) Coordination with related actions pending in one or more courts in other counties, states, or countries, or in a federal court; or
(5) Substantial postjudgment judicial supervision. (Subd (b) amended effective January 1, 2007.)
(c) Provisional designation Except as provided in (d), an action is provisionally a complex case if it involves one or more of the following types of claims:
(1) Antitrust or trade regulation claims;
(2) Construction defect claims involving many parties or structures;
(3) Securities claims or investment losses involving many parties;
(4) Environmental or toxic tort claims involving many parties;
(5) Comprehensive adjudications of groundwater rights;
(6) Claims involving mass torts;
(7) Claims involving class actions; or
(8) Insurance coverage claims arising out of any of the claims listed in (c)(1) through (7). (Subd (c) amended effective January 1, 2026; previously amended effective January 1, 2007.)
(d) Court’s discretion Notwithstanding (c), an action is not provisionally complex if the court has significant experience in resolving like claims involving similar facts and the management of those claims has become routine. A court may declare by local rule that certain types of cases are or are not provisionally complex under this subdivision. (Subd (d) amended effective January 1, 2007.)
Plain-English Summary
Some lawsuits need more hands-on management than a standard case calendar allows: more motions, more parties, more documents, more coordination with other courts. Rule 3.400 gives that category of case a name — "complex case" — and a working definition: an action that needs exceptional judicial management to avoid overburdening the court and the litigants, while still moving toward a resolution and keeping costs under control. In deciding whether a case fits, a court weighs things like the number of difficult pretrial motions expected, the volume of witnesses or documents involved, how many separately represented parties there are, whether related cases are pending elsewhere, and whether the case will need substantial supervision after judgment.
Rather than leaving every case to a fresh, individualized analysis, Rule 3.400(c) fast-tracks certain kinds of claims into complex status from the outset: antitrust and trade regulation claims, large construction defect cases, securities and investment-loss claims involving many parties, environmental or toxic tort claims involving many parties, comprehensive groundwater rights adjudications, mass torts, class actions, and insurance coverage disputes tied to any of those. Filing one of those claims puts a case on the complex track provisionally, without waiting for a case-by-case finding.
That provisional label is not automatic in every court, though. A court with real experience handling a particular type of claim can decide, case by case or by local rule, that its own routine handling of that claim type means the case is not provisionally complex after all — recognizing that what counts as "exceptional" management depends in part on how unusual the case is for that particular court.
Frequently Asked Questions
What makes a California civil case a 'complex case'?
Rule 3.400(a) defines a complex case as one that requires exceptional judicial management to avoid unnecessary burdens on the court and litigants while keeping the case moving and costs reasonable.
Which types of claims are automatically treated as provisionally complex?
Rule 3.400(c) lists antitrust and trade regulation claims, large construction defect cases, securities or investment-loss claims involving many parties, environmental or toxic tort claims involving many parties, comprehensive groundwater rights adjudications, mass torts, class actions, and related insurance coverage claims.
Can a court decide a case isn't complex even if it falls on the provisional list?
Yes. Under Rule 3.400(d), a court with significant experience handling similar claims can treat that category as routine and not provisionally complex, including by local rule.
What factors does a court consider when deciding complex status outside the provisional categories?
Rule 3.400(b) points to the likely number of difficult pretrial motions, the volume of witnesses or documents, the number of separately represented parties, coordination with related actions elsewhere, and the need for substantial postjudgment supervision.
Amendment History
Rule 3.400 amended effective January 1, 2026; adopted as rule 1800 effective January 1, 2000; previously amended and renumbered effective January 1, 2007.
Source & verification. Rule text is reproduced verbatim from
the Judicial Council of California. Adopted by the Judicial Council of California.
Last verified July 29, 2026.
· Official source
Also known as: what is a complex case california courtrule 3.400 complex litigation definitionprovisionally complex case types californiacomplex civil litigation program california