The search engine giant-turned-media group has launched an experimental video site offering access to professionally made content funded entirely by advertising.
Users can watch Alfred Hitchcock's The 39 Steps or a classic Charlie Chaplin sketch in a window under an advert for Netflix, or relive the animated adventures of Mr Magoo or Rocky and Bullwinkle under a banner ad for Burger King.
Hewlett-Packard, the computer maker, is also among the half-dozen advertisers to have signed up to the trial.
Google Video had previously offered access to film and television content for a small fee, but its entry into the free-to-air market was being seen yesterday an important moment in the explosion of video on the web.
Placing adverts on online video could also become a big new revenue stream for Google, which currently makes most of its profits from adverts posted next to queries to its search engine.
A Google spokesman said: "We are always looking for ways to show targeted and engaging advertising to users and we think that Google Video is a natural extension of this ongoing effort."
Broadcasters have been fretting over the explosion in internet video over the past year, which threatens to become a major challenge to network television and lucrative DVD sales. Several broadcasters have begun selling downloadable version of their shows over iTunes and other online stores. And earlier this year, Disney-owned ABC, maker of Desperate Housewives and Lost, experimented with free online streaming of some shows, including advert breaks that viewers could not skip.
The jury is still out on whether internet users will agree to pay for download-to-own videos or one-time streaming, or whether an advertisement-funded model will prevail. Google characterised its move into free video as a trial, and it continues to have feet in both camps.
Looking on nervously will be Steve Jobs, chairman of Apple, whose iTunes looks set to be the biggest retailer of video downloads if a paid-for model wins out. The iTunes store has sold more than 15 million videos in the nine months since it added the content.
An explosion of free user-generated content such as amateur videos, available on sites such as YouTube, is encouraged people, especially teenagers, to spend more time on the internet.