Out of the many immunities and exemptions precluding or limiting the application of antitrust laws in the United States, state action may be the most widely relied upon immunity. It offers numerous state and local government entities immunity from federal antitrust law challenges. In a rare and much-anticipated decision, the Supreme Court recently explained and limited the application of this immunity where private parties purport to act pursuant to government authority. This ruling invigorated and encouraged other lawsuits, and will likely inspire litigants to continue to bring claims against government entities into the immediate future. These emerging cases, however, also offer valuable guidance to government entities on how to avoid antitrust problems.