December 4, 2018 Scott Behrens Chief Financial Officer ACI WORLDWIDE, INC. 3520 Kraft Rd., Suite 300 Naples, FL 34105 Re: ACI WORLDWIDE, INC. Form 10-K for the Fiscal Year Ended December 31, 2017 Filed February 27, 2018 Form 10-Q for the Quarterly Period Ended March 31, 2018 Filed May 10, 2018 File No. 000-25346 Dear Mr. Behrens: We have completed our review of your filings. We remind you that the company and its management are responsible for the accuracy and adequacy of their disclosures, notwithstanding any review, comments, action or absence of action by the staff. Sincerely, Division of Corporation Finance Office of Information Technologies and Services