The Constitutions Census Clause authorizes Congress to direct an "actual Enumeration" of the American public every 10 years to provide a basis for apportioning congressional representation among the States. Pursuant to this authority, Congress has enacted the Census Act (Act), 13 U. S. C. §1 et seq., delegating the authority to conduct the decennial census to the Secretary of Commerce (Secretary). The Census Bureau (Bureau), which is part of the Department of Commerce, announced a plan to use two forms of statistical sampling in the 2000 Decennial Census to address a chronic and apparently growing problem of "undercounting" of some identifiable groups, including certain minorities, children, and renters. In early 1998, two sets of plaintiffs filed separate suits challenging the legality and constitutionality of the plan. The suit in No. 98-564 was filed in the District Court for the Eastern District of Virginia by four counties and residents of 13 States. The suit in No. 98-404 was filed by the United States House of Representatives in the District Court for the District of Columbia. Each of the courts held that the plaintiffs satisfied the requirements for Article III standing, ruled that the Bureaus plan for the 2000 census violated the Census Act, granted the plaintiffs motion for summary judgment, and permanently enjoined the planned use of statistical sampling to determine the population for congressional apportionment purposes. On direct appeal, this Court consolidated the cases for oral argument.

Held:

1. Appellees in No. 98-564 satisfy the requirements of Article III standing. In order to establish such standing, a plaintiff must allege personal injury fairly traceable to the defendants allegedly unlawful conduct and likely to be redressed by the requested relief. E.g., Allen v. Wright, 468 U. S. 737, 751. A plaintiff must establish that there exists no genuine issue of material fact as to justiciability or the merits in order to prevail on a summary judgment motion. See, e.g., Lujan v. National Wildlife Federation, 497 U. S. 871, 884. The present controversy is justiciable because several of the appellees have met their burden of proof regarding their standing to bring this suit. In support of their summary judgment motion, appellees submitted an affidavit that demonstrates that it is a virtual certainty that Indiana, where appellee Hofmeister resides, will lose a House seat under the proposed census 2000 plan. That loss undoubtedly satisfies the injury-in-fact requirement for standing, since Indiana residents votes will be diluted by the loss of a Representative. See, e.g., Baker v. Carr, 369 U. S. 186, 208. Hofmeister also meets the second and third standing requirements: There is undoubtedly a "traceable" connection between the use of sampling in the decennial census and Indianas expected loss of a Representative, and there is a substantial likelihood that the requested relief--a permanent injunction against the proposed uses of sampling in the census--will redress the alleged injury. Appellees have also established standing on the basis of the expected effects of the use of sampling in the 2000 census on intrastate redistricting. Appellees have demonstrated that voters in nine counties, including several of the appellees, are substantially likely to suffer intrastate vote dilution as a result of the Bureaus plan. Several of the States in which the counties are located require use of federal decennial census population numbers for their state legislative redistricting, and States use the population numbers generated by the federal decennial census for federal congressional redistricting. Appellees living in the nine counties therefore have a strong claim that they will be injured because their votes