ATG Joins Russell 3000 Index.

CAMBRIDGE, Mass. -- ATG (Art Technology Group, Inc., NASDAQ: ARTG), whose licensed and on demand technology powers e-commerce sites and corresponding e-marketing and customer service for the world's most customer-centric enterprises, today announced that it will be added to the Russell 3000 Index when Russell Investment Group reconstitutes its family of U.S. indexes on June 30.

Membership in the Russell 3000, which remains in place for one year, means automatic inclusion in the large-cap Russell 1000(R) Index or small-cap Russell 2000(R) Index as well as the appropriate growth and style indexes. Russell determines membership for its equity indexes primarily by objective, market capitalization rankings and style attributes.

"We are pleased by the broader financial community awareness that will be generated by ATG's inclusion in the Russell 3000," said Julie Bradley, SVP and chief financial officer, ATG. "As selling on the Web continues to become a larger part of more and more businesses, we are optimistic about the continued demand for our market-leading licensed and OnDemand e-commerce applications."

Russell indexes are widely used by investment managers and institutional investors for index funds and as benchmarks for both passive and active investment strategies. An industry-leading $3.8 trillion in assets currently is benchmarked to them. Investment managers who oversee these funds purchase shares of member stocks according to that company's weighting in the particular index.

The Russell 3000 Index offers investors access to the broad U.S. equity universe representing approximately 98% of the U.S. market. The Russell 3000 is constructed to provide a comprehensive, unbiased, and stable barometer of the broad market and is completely reconstituted annually to ensure new and growing equities are reflected.

About ATG

ATG (Art Technology Group, Inc., NASDAQ: ARTG) makes the software that the world's most customer-conscious companies use to create a more relevant and consistent customer experience, throughout the marketing, commerce, and service lifecycle, and across the Web, e-mail, call center, and mobile channels. Offering an alternative to the traditional silo-based approach to customer-facing applications, ATG Wisdom(TM) is the company's strategy for delivering a seamless, more compelling, and mutually valuable experience to each customer and segment. The company fulfills this strategy by providing fully integrated best-of-breed product suites installed on-premise or delivered on-demand. ATG's solutions power over 600 major brands, including A&E Networks, Airbus, American Airlines, American Eagle Outfitters, Best Buy, Boeing, Cingular Wireless, DirecTV, France Telecom, Friends Provident, Hewlett-Packard, Hotels.com, Hyatt Hotels, HSBC, InterContinental Hotels Group, Kingfisher, Louis Vuitton, Merrill Lynch, Neiman Marcus, Philips, Procter & Gamble, Symantec, T-Mobile, Target, US Army, US Navy, Warner Music, and Wells Fargo. 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.

(C) 2006 Art Technology Group, Inc. ATG and Art Technology Group are registered trademarks, and ATG Wisdom is a trademark of Art Technology Group, Inc. All other product names, service marks, and trademarks mentioned herein are trademarks of their respective owners.

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 its 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 will not increase customer revenue across brands; that those customers leveraging ATG will not 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.