Google and the Nielsen Company announced today a multi-year, strategic relationship. As a first step, the relationship leverages Nielsen’s experience in television audience measurement to bring demographic data to the Google TV Ads advertising platform.

By combining Nielsen demographic data with aggregated set-top box data, Google hopes to provide advertisers and agencies with comprehensive information to help them create better ads for viewers and maximize the return on their advertising spending.

“As we continue to expand our TV advertising program, it is important that we provide advertisers and agencies with data that will help them reach their target demographic with the right ad,” said Eric Schmidt, chief executive officer at Google. “Working closely with Nielsen, the industry leader, improves our measurement capabilities by adding a demographic layer on top of existing set-top box data. We’re pleased that Nielsen is working with us in this endeavor.”

The partnership reflects broader trends of using technology to deliver more intelligent, targeted video advertising and the integration of online and offline data.

Google TV Ads is an online platform for buying, selling, measuring and delivering television ads. The platform, which has been operational since May, includes advertising inventory across hundreds of channels and all dayparts. A key benefit of Google TV Ads is the ability to report second-by-second set-top box data so advertisers can evaluate the reach of an ad and only pay for actual set-top box impressions. Advertisers can better understand exactly how their ad is performing and make near real time changes to their TV advertising campaigns to deliver better ads to viewers. Data derived from Nielsen’s representative television ratings panels will provide Google TV Ads advertisers with the demographic composition of the audience.

This is the first time that advertisers and agencies will have this level of detailed measurement available in a single place and at such a large scale. This information is available through the existing Google AdWords report center and can be accessed 24 hours after an ad has aired.

Moving forward, Google and Nielsen plan to explore a number of other opportunities to work together to measure online and other media. Additional details of the agreement were not disclosed.