In their Articles, Professors Langevoort and Miller each address the problem of defining market efficiency for fraud-on-the-market purposes in the wake of Halliburton Co. v. Erica P. John Fund, Inc. (“Halliburton II”). As their analyses highlight, the fundamental difficulty of the fraud-on-the-market doctrine is its fuzziness around the edges–there are few guideposts for how broadly or narrowly it should apply. Until now, courts have dealt with this fuzziness by adopting an extremely narrow definition of market efficiency. Halliburton II, however, appears to alter the balance by broadening the concept of market efficiency, while simultaneously permitting district courts to police the application of the fraud-on-the-market doctrine on a case-by-case basis. It remains to be seen how much Halliburton II will change the legal landscape, but what is certainly true is that district courts will continue to search for ways to cabin the doctrine’s potential scope.