On November 15, the U.S. Supreme Court agreed to hear a challenge to the long-standing “fraud-on-the-market” theory, on which securities class actions often are based. Halliburton v. Erica P. John Fund Inc., No. 13-317, 2013 WL 4858670 (Nov. 15, 2013). Halliburton petitioned the Court after an appeals court relied on the theory to affirm class certification in a securities suit against the company, even after the appeals court acknowledged that no company misrepresentation affected its stock process. As explained in the petition, the theory at issue derives from the Court’s holding in Basic Inc. v. Levinson, 485 U.S. 224 (1988) that a putative class of investors should not be required to prove that they actually relied in common on a misrepresentation in order to obtain class certification and prevail on the merits. The petitioner argues that Basic instead allows putative class members to invoke a classwide presumption of reliance based on the concept that all investors relied on the misrepresentations when they purchased stock at a price distorted by those misrepresentations. Halliburton has asked the Court to determine (i) whether the Court should overrule or substantially modify the holding of Basic, to the extent that it recognizes a presumption of classwide reliance derived from the fraud-on-the-market theory; and (ii) whether, in a case where the plaintiff invokes the presumption of reliance to seek class certification, the defendant may rebut the presumption and prevent class certification by introducing evidence that the alleged misrepresentations did not distort the market price of its stock.