On June 6, 2011, in Erica P. John Fund, Inc. v. Halliburton Co., the Supreme Court unanimously held that private securities fraud plaintiffs do not need to prove loss causation in order to obtain class certification.  The high court drew a firm line between two separate elements of a private securities fraud claim: (1) reliance on alleged misrepresentations or omissions, and (2) loss causation.  In a guest article, Jonathan K. Youngwood and Joseph M. McLaughlin, litigation partners with Simpson Thacher & Bartlett LLP in New York, discuss the factual and procedural background of the decision, the Supreme Court’s legal analysis and the implications of the decision for private securities fraud litigation.