This Deal Helped Turn Google Into an Ad Powerhouse. Is That a Problem?

Google owns the world’s leading search engine, it operates the largest video-hosting service in YouTube, and its popular web browser, email, map and meeting software is used by billions of people.

But its financial heft — the source of nearly all its enormous profits — is advertising. And perhaps no day was more pivotal in transforming Google into a powerhouse across the entire digital advertising industry than April 13, 2007, when the company clinched a deal to buy DoubleClick for $3.1 billion.

The deal turned out to be “a total game changer, a crucial piece in the larger jigsaw puzzle Google put together,” said Timothy Armstrong, a former Google executive who championed the acquisition.

It has also turned out to be a classic example of why a growing number of antitrust experts say lawmakers need to broadly rethink how mergers are regulated when the buyer is a tech company with strong and growing market power.

Google’s ad business is now a focus of wide-ranging investigations by the Justice Department and state attorneys general. The scrutiny includes whether the company choked off competitors, or shortchanged advertisers and publishers, and how it assembled its ad empire, including DoubleClick, an ad technology company and marketplace.