Advertising.com Japan will be a joint venture between the AOL unit and Mitsui & Co., Ltd., designed to try to tap in to the growing online ad market there. Advertising.com, the #3 display ad network in the U.S., has operations in eight Uk/European countries. Advertising.com will provide proprietary ad serving and optimization technology; Mitsui has relationships with Japanese advertisers and publishers. No financial terms disclosed. Release.