Environmental groups sued to force the Interior Secretary to apply the Endangered Species Act to federally funded projects abroad. Their members alleged they intended, someday, to revisit affected regions and observe threatened species. Justice Scalia's opinion held that 'some day' intentions do not amount to concrete, particularized injury. He crystallized the standing doctrine into three elements: (1) an injury in fact that is concrete, particularized, and actual or imminent; (2) a causal connection to the challenged conduct; and (3) a likelihood that the injury will be redressed by a favorable decision. Lujan is now the first citation in virtually every federal-court standing analysis and a critical gatekeeper on public-interest litigation.