Ann T.Rossum


Irvine + 1.949.553.7530

Ann Rossum's practice focuses on commercial litigation, with an emphasis in class action defense. Her practice has included prosecuting and defending claims involving cybersecurity and data protection, consumer fraud and false advertising, trade secrets misappropriation, health care, antitrust, contract disputes, and the Fair Credit Reporting Act. Ann is experienced in all aspects of litigation, including trial.

Ann's recent matters include obtaining a multimillion dollar jury verdict, including punitive damages, on behalf of two large commercial insulation companies asserting misappropriation of trade secrets claims. She also represented a health care provider in parallel federal and state class actions that alleged tying and market leveraging. Ann's work in these matters focused on motion practice and pretrial preparation. Additionally she represented Applied Medical in an action in which it obtained a $33 million U.S. judgment and an anti-suit injunction precluding litigation in South Korea. Ann also has represented Experian Information Solutions in a wide range of matters at the trial and appellate court levels, including in multiple actions in which Experian obtained complete victories on summary judgment that were affirmed on appeal.

Ann also devotes significant time to pro bono work through Jones Day's Laredo Project, which provides assistance to detained refugees.

Before joining Jones Day, Ann clerked for the Honorable Marilyn L. Huff in the United States District Court for the Southern District of California. She is a member of the State Bar of California, the Association of Business Trial Lawyers, and the Orange County Bar Association.


  • 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.
  • Sutter Health defends antitrust suitsJones Day represents Sutter Health in two antitrust suits brought by putative classes alleging that Sutter has conspired to violate the state and federal antitrust laws with respect to Sutter's provision of health care services in Northern California.
  • 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 statusAnn Rossum and Roman Darmer of the Irvine Office 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.
  • Speaking Engagements

    • 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
    We use cookies to deliver our online services. Details of the cookies and other tracking technologies we use and instructions on how to disable them are set out in our Cookies Policy. By using this website you consent to our use of cookies.