Yahoo! today announced that it has entered into a definitive agreement to acquire Right Media Inc., creator of the Right Media Exchange.

Under the terms of the agreement, which follows Yahoo!'s 20 percent strategic investment in Right Media in October 2006, Yahoo! will acquire the remaining equity interest in Right Media for approximately $680 million.

"The acquisition of Right Media will further Yahoo!'s goal to create the industry's most open, accessible and vibrant advertising marketplace, which will help democratize the buying and selling of digitally enabled advertising," said Terry Semel, chairman and CEO of Yahoo!.

The announcement comes just a few weeks after DoubleClick agreed to be acquired by Google for $3.1 billion. Since that deal, some analysts have speculated that Yahoo would acquire control of Right Media to help it compete against the Google-DoubleClick alliance.

Yahoo said that after the acquisition it would increase its participation in the exchange as both a buyer and seller of ads. The company said it planned eventually to sell all the nonpremium ad space on Yahoo through the exchang.

The deal will give advertisers more choices of where to place ads and will allow publishers to sell their own advertising inventory alongside Yahoo's, they said. Yahoo executives said that about 1,000 publishers are using Right Media to sell ad space on their sites.