Before undertaking a major federal action significantly affecting the environment, an agency generally must prepare an environmental impact statement analyzing the action's direct, indirect, and cumulative effects and a reasonable range of alternatives, including a no-action alternative. Agencies may instead prepare a shorter environmental assessment and, if it supports a finding of no significant impact, avoid the full EIS process — whether that threshold determination was proper is itself a common point of challenge.

Courts review EIS adequacy under the arbitrary-and-capricious standard, applying what is often called a hard look requirement: the agency must have genuinely engaged with the relevant environmental consequences and reasonable alternatives, even though courts do not independently weigh the environmental costs and benefits themselves. Frequent grounds for challenge include an unreasonably narrow definition of connected actions, inadequate cumulative impact analysis, and failure to consider a reasonable alternative.

The typical remedy for a successful EIS challenge is vacatur of the agency's decision and remand for further analysis, not a permanent bar on the underlying project, which means litigation often functions to delay and reshape a project rather than to stop it outright. A Juricratic simulation can model the range of remand outcomes — full vacatur, partial remand, or an agency reissuing a corrected EIS — as branching scenarios to rehearse project timeline and cost exposure under each.

EIS challenges are typically filed by project opponents against the lead federal agency after a final EIS or record of decision is issued, with litigation focused on whether the agency adequately analyzed cumulative impacts, connected actions, and reasonable alternatives, and commonly resulting in a remand rather than outright project cancellation.