Intervention
A procedure allowing a nonparty to join an existing lawsuit because the case may affect its interests.
Governing rule: Fed. R. Civ. P. 24
Plain-English definition
Intervention lets an outsider become a party when the litigation threatens an interest the outsider needs to protect. Some intervention is by right; other intervention is discretionary. Courts look at timing, interest, impairment, and whether existing parties adequately represent the applicant.
How it works
The proposed intervenor files a motion and usually attaches the pleading it wants to file. Delay can defeat intervention even when the interest is serious.
Why it matters
Intervention can bring regulators, insurers, advocacy groups, competitors, or affected property owners into high-stakes litigation.