World's Leading Luxury Retail Products Brand Re-Invests in ATG Customer Experience Platform

Louis Vuitton continues to drive sales with ATG solutions

CAMBRIDGE, Mass., May 23, 2005 - ATG (Art Technology Group, Inc. NASDAQ: ARTG), the software provider behind the most consistent and relevant marketing, commerce, and service experiences, today announced that Louis Vuitton, one of the world's leading luxury retail product brands, has again selected ATG technology as it continues to drive sales through its online storefronts on the ATG Customer Experience Platform.

Louis Vuitton selected ATG for its adaptable, proven technology and demonstrated industry knowledge in helping companies market and sell more effectively online to their customers. The company uses commerce and marketing elements of the ATG platform to target content more effectively to multiple audiences and drive up-sell and cross-sell opportunities, which ultimately helps Louis Vuitton increase average order size and revenues.

"Louis Vuitton is clearly one of the most recognizable and operationally sound luxury brands in retailing," said Cliff Conneighton, senior vice president of marketing, ATG. "ATG is thrilled that Louis Vuitton has made the decision to drive their next-generation customer experience with ATG technology. ATG Commerce provides the most comprehensive online selling solution on the market, and we're well positioned to partner with Louis Vuitton and achieve even greater levels of success."This announcement comes on the heels of ATG's recent number one rating in e-commerce/e-marketing by both of the leading market research firms, Gartner and Forrester.

About ATG
ATG (Art Technology Group, Inc., NASDAQ: ARTG) delivers innovative software to help high-end consumer-facing companies create a richer, more adaptive interactive experience for their customers and partners throughout the lifecycle of marketing, commerce, and customer service, and across the Web, e-mail and call centers. ATG has delivered category-leading e-business solutions to many of the world's best known brands including A&E Networks, Airbus, American Airlines, American Eagle Outfitters, AT&T Wireless, Best Buy, Boeing, France Telecom, Friends Provident, GE, Hewlett-Packard, HSBC, InterContinental Hotels Group, Kingfisher, Merrill Lynch, Neiman Marcus, Philips, Procter & Gamble, SBC, T-Mobile, Target, US Army, US Federal Aviation Administration, Wells Fargo, Warner Music, and Yahoo! The company is headquartered in Cambridge, Massachusetts, with additional locations throughout North America, Europe, and Asia. For more information about ATG, please visit www.atg.com.

©2005 Art Technology Group, Inc. ATG and Art Technology Group are registered trademarks of Art Technology Group, Inc., and ATG Campaign Optimizer is its service mark. All other product names, service marks, and trademarks mentioned herein are trademarks of their respective owners.

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This press release contains forward-looking statements for purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. These statements involve known and unknown risks and uncertainties that may cause ATG's actual results, levels of activity, performance or achievements to be materially different from any future results, levels of activity, performance or achievements expressed or implied by such forward-looking statements. Important risk factors affecting ATG's business generally may be found in their periodic reports and registration statements filed with the Securities and Exchange Commission at www.sec.gov. Risk factors related to the subject matter of this press release include the possibility that the ATG product deployment will not be successful, on time or significantly enhance the user's Internet experience or handle user volumes; that those customers leveraging ATG won't have the opportunity to increase revenue and decrease future costs; the need to adapt to rapid changes so products do not become obsolete; the possibility of errors in ATG's software products; the possibility that the solution will not make customer implementations faster or more flexible or permit the customer to meet its customer-facing or infrastructure requirements; that the ATG product will not continue to be integrated with third party applications servers or will not support all Web services enabled systems; that ATG's product strategy may change in the future; and the risks and costs of intellectual property litigation. ATG undertakes no obligation to update any of the forward-looking statements after the date of this press release.

Tucker Walsh
ATG
+1.617.386.1159
twalsh@atg.com