On June 23, in Halliburton Co. v. Erica P. John Fund, Inc., 134 S. Ct. 2398 (2014) (No. 13-317), the United States Supreme Court re-evaluated, but declined to overrule, its prior ruling in Basic Inc. v. Levinson, 485 U.S. 224 (1988), that plaintiffs could prevail on a Securities Act claim under Section 10(b) and Rule 10(b)(5) based on the “fraud on the market” theory. In addition, as is relevant to class certification, the Court held that while plaintiffs may try to rely on the fraud on the market presumption to prove reliance, defendants may attempt to defeat the presumption at the class certification stage by presenting evidence that the alleged misrepresentation did not affect the stock price. As applied to securities cases, the rigorous analysis undertaken at the class certification stage permits parties opposing the fraud on the market theory to submit evidence undermining the claim of price impact. While Basic permits the presumption, it does not require district courts to ignore direct evidence showing that the alleged misrepresentation did not affect the stock price, such that the presumption is rebutted.