Under an agreement to be announced today, Google will pay Nielsen an undisclosed amount to obtain detailed information about the kinds of people who watch specific TV shows.
New York-based Nielsen has been selling demographic data to television stations and advertisers for years.
Google's access to the information is significant because it gives the Mountain View, Calif., company more tools to use as it tries to target TV ads as effectively as it has done on the Internet.
"This is another indication that Google is very serious about selling more ads in the mainstream media," said Brad Adgate, director of research for Horizon Media, which helps advertisers buy TV ads.
Since May, Google has been delivering television ads for about 14 million subscribers to EchoStar Communications Corp.'s Dish network and Astound Broadband cable service.
The set-top boxes used by EchoStar and Astound enabled Google to track when commercials were watched and for how long. By drawing on Nielsen's data, Google will now have information on what kinds of viewers watch a particular commercial.
"This was a missing piece of the puzzle for us," said Keval Desai, Google's director of product management for TV ads.
The Google deal appeals to Nielsen because the rating firm is trying to develop new measurement techniques and extend its reach into such digital media as iPods and cellphones.