Court of Appeals concluded that the District Court had not abused its discretion in applying that doctrine against the United States in this case. 672 F. 2d 1320, 1322 (1982). The Court of Appeals rejected the Government’s argument that Parklane Hosiery should be limited to private litigants. Although it acknowledged that the Government is often involved in litigating issues of national significance where conservation of judicial resources is less important than “getting a second opinion,” it concluded that litigation concerning the rights of Filipino war veterans was not such a case. 672 F. 2d, at 1329-1330. For the reasons which follow, we agree with the Government that Parklane Hosiery's approval of nonmutual offensive collateral estoppel is not to be extended to the United States.
Under the judicially developed doctrine of collateral estop-pel, once a court has decided an issue of fact or law necessary to its judgment, that decision is conclusive in a subsequent suit based on a different cause of action involving a party to the prior litigation. Montana v. United States, 440 U. S. 147, 153 (1979). Collateral estoppel, like the related doctrine of res judicata,3 serves to “relieve parties of the cost and vexation of multiple lawsuits, conserve judicial resources, and, by preventing inconsistent decisions, encourage reliance on adjudication.” Allen v. McCurry, 449 U. S. 90, 94 (1980). In furtherance of those policies, this Court in recent years has broadened the scope of the doctrine of collateral estoppel beyond its common-law limits. Ibid. It has done so by abandoning the requirement of mutuality of parties, Blonder - Tongue Laboratories, Inc. v. University of Illinois Foundation, 402 U. S. 313 (1971), and by conditionally approving the
3
Under res judicata, a final judgment on the merits bars further claims by parties or their privies on the same cause of action. Montana v. United States, 440 U. S., at 153; Parklane Hosiery Co. v. Shore, 439 U. S. 322, 326, n. 5 (1979). The Restatement of Judgments speaks of res judi-cata as “claim preclusion” and of collateral estoppel as “issue preclusion.” Restatement (Second) of Judgments § 27 (1982).