Ann T.Rossum


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Ann Rossum's practice focuses on representing companies in high-stakes litigation. She has prosecuted and defended proceedings spanning multiple subject matters and industries. She has litigated product liability, false claims, trade secrets, health care, antitrust, contracts, and consumer protection matters. Ann has substantial trial and arbitration experience and is skilled in all aspects of litigation.

Ann's recent matters include defending a major retailer in multiple cases brought by states and municipalities alleging that the distribution and sale of prescription opioids constitutes a public nuisance, as well as defending a Northern California hospital system in a substantial antitrust class action alleging the system restrained competition via its contracts with insurance companies. Her recent accolades include securing a multimillion dollar jury verdict in a trade secret misappropriation lawsuit and briefing and arguing numerous successful dispositive and discovery motions, several of which were subject to and affirmed on appeal.

Ann regularly contributes to her community. She provides pro bono legal assistance to detained refugees through Jones Day's Border Project and serves on the Board of Directors for the Public Law Center. Ann is a member of the State Bar of California and the Orange County chapter of the Association of Business Trial Lawyers. Ann is the hiring partner for the Firm's Irvine Office and leads the Irvine Office's Women's Affinity Group.


  • Sutter Health wins complete defense verdict in landmark antitrust class actionJones Day won a complete defense jury verdict for Sutter Health in a landmark antitrust class action seeking $1.2 billion in treble damages.
  • CafePress obtains complete dismissal of putative nationwide class action relating to data breachJones Day obtained a complete dismissal of a putative nationwide class action arising from an alleged data breach on behalf of CafePress Inc. (now known as Residual Pumpkin Entity, LLC).
  • Experian secures pleading-stage dismissal in CARES Act-related class actionJones Day secured a pleading-stage dismissal for Experian Information Solutions, Inc. in a class action arising out of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act.
  • Procter & Gamble defeats class certification in misbranding actionJones Day obtained complete denial of class certification in a putative consumer class action brought against The Procter & Gamble Company in which the plaintiffs alleged that the labeling of Pringles potato crisps is false and misleading.
  • Experian forecloses class and forensic discovery, precluding nationwide class claimsJones Day, on behalf of Experian Information Solutions, Inc., obtained dismissal of a motion to compel class and technical/forensic discovery of Experian’s computer systems in a nationwide class action.
  • Experian prevails on summary judgment, granted attorney’s fees in case involving serial plaintiffJones Day client Experian Information Solutions, Inc. prevailed on a motion for summary judgment in a credit reporting dispute.
  • TransDigm defends putative class action lawsuit over allegedly defective spark plugsJones Day is defending TransDigm Group Incorporated subsidiary Champion Aerospace, LLC against a putative class action lawsuit alleging, on behalf of general aviation aircraft owners in California, that certain Champion Aerospace spark plugs are defective.
  • Experian prevails on motion to dismiss/terminate arbitration proceedings before AAA and United States District Court confirmsOn December 26, 2017, Jones Day, on behalf of Experian Information Solutions, Inc. ("Experian"), obtained a complete dismissal and termination Order from Arbitrator Roland M. Cavalier of the American Arbitration Association ("AAA") of Plaintiff Brian Berger’s claims.
  • Experian obtains dismissal of class actionJones Day, on behalf of Experian Information Solutions, Inc., recently obtained a complete dismissal with prejudice of putative class claims arising under the Fair Credit Reporting Act (“FCRA”) brought by a repeat plaintiffs’ firm on behalf of Lynn Travers and a putative nationwide class.
  • Experian obtains summary judgment in purported class action alleging violation of Fair Credit Reporting Act based on reporting of payday loansJones Day client Experian Information Solutions, Inc. (“Experian”) obtained a complete victory on summary judgment against a plaintiff purporting to represent a nationwide putative class alleging violations of the Fair Credit Reporting Act, 15 U.S.C. § 1681e(b), based on Experian’s reporting of payday loans that Plaintiff contended were unlawful.
  • Distribution International and E.J. Bartells obtain complete victory in trade secrets misappropriation actionJones Day clients Distribution International Southwest, LLC and Rhem, LLC, d/b/a E.J. Bartells, two large commercial insulation distributors, obtained a unanimous, favorable jury verdict following a trial in the District Court of Denver, Colorado.
  • Applied Medical obtains $33 million judgment in cross-border business disputeAfter nearly three years of protracted litigation, Jones Day client Applied Medical Distribution Corporation obtained a damages award and judgment exceeding $33 million against a South Korean corporation, Ah Sung International, Inc., and its President/majority shareholder, and senior director.
  • Experian obtains confirmation of final arbitration award in dispute with repeat litigantJones Day client Experian Information Solutions, Inc. obtained confirmation of a final arbitration award in its favor in a dispute brought by a repeat litigant alleging violations of the Fair Credit Reporting Act.
  • Experian prevails in Tenth Circuit appealJones Day client Experian Information Solutions, Inc. obtained a Tenth Circuit decision affirming a summary judgment in Experian's favor in litigation over fraud-based and Fair Credit Reporting Act claims.
  • R.J. Reynolds resolves long-running class action over unfair competition claimsJones Day client R.J. Reynolds Tobacco Company obtained a settlement resolving a nationwide consumer class action involving consumer promotional programs. R.J. Reynolds originally obtained dismissal of the case under Rule 12.
  • Procter & Gamble achieves dismissals with prejudice of two putative class action lawsuits over advertising for batteriesJones Day successfully defended The Procter & Gamble Company (P&G) and its subsidiary The Gillette Company in two statewide consumer class actions in California and Massachusetts concerning Duracell AA and AAA Coppertop batteries.
  • Lennar resolves putative product liability and consumer fraud class action lawsuitsJones Day client Lennar Corporation obtained the voluntary dismissal of putative class action lawsuits against Lennar homebuilding subsidiaries in California and the settlement of nationwide putative class action lawsuits in Nevada and Minnesota after defeating bids for class certification, and defeating plaintiffs' attempt to appeal to the Ninth Circuit in the Nevada case.
  • Newspaper published by legal aid first in nation to obtain general circulation statusJones Day represented the Legal Aid Society of Orange County in obtaining orders adjudicating its weekly publication, "The Notice," as a newspaper of general circulation in Orange and Los Angeles Counties.
  • Lennar defeats certification in two California class actions regarding allegedly defective "yellow brass" fittingsJones Day represented two California subsidiaries of the homebuilder Lennar Corporation in separate but similar statewide class actions regarding high-zinc-content brass fittings (often called "yellow brass" fittings) that were alleged to corrode through a chemical reaction called dezincification when exposed to water, ultimately causing the fittings to occlude or leak.
  • Lennar defeats certification in consolidated class action involving allegedly defective "yellow brass" plumbing fittingsJones Day represented two subsidiaries of the homebuilder Lennar Corporation in connection with a consolidated class action regarding high-zinc-content brass plumbing fittings (often called "yellow brass" fittings) that were alleged to corrode through a chemical reaction called dezincification when exposed to water, ultimately causing the fittings to occlude or leak.
    • January 26, 2022
      What a Nuisance! How Traditional Products Liability Law Is Being Swallowed by an Expansive Interpretation of Public Nuisance and What Corporate Defendants Can Do About It, Jones Day MCLE University
    • January 22, 2020
      Recent Trends in Class Action Settlements, Jones Day MCLE University
    • July 17, 2018
      Data Privacy: Customer Privacy v. Customer Profiling for Marketing Purposes, Jones Day Seminar