This summer, Google will begin demonstrating what may be its most potent weapon in this emerging battle: an overhauled version of the advertising exchange that it picked up in the $3.2 billion acquisition of DoubleClick last year. Ad exchanges are sort of like stock exchanges for online ads. Web sites put ad space up for auction, and ad agencies, armed with demographic and behavioral data about the people who visit those sites, bid to place ads for their clients' campaigns. Yahoo, Microsoft, and others also run exchanges.

Until now, Google's and DoubleClick's ad-placement systems used different software, so ad agencies had to cobble together programs to place, monitor, and measure ads. In the revamped exchange, they'll be able to use the two systems seamlessly, making ad buys simpler. At the same time, Google is pushing Web publishers, which have been wary of putting prime ad space on the exchange for fear of turning it into a low-value commodity, to pony up more space. In return, Google is expected to give Web publishers more control over pricing and who can bid on the space.

Google's Grab for the Display Ad Market - BusinessWeek