Miguel Helft has been a senior writer at Fortune since 2011, writing frequently about technology.
Last week, the Federal Trade Commission closed its investigation of Google's search business. That ends the most significant antitrust probe the company has faced so far. But it's not the first time Google has come under the scrutiny of antitrust regulators in the United States, nor is it likely to be the last. Google, whose search business is still the subject of antitrust inquiries in Europe and elsewhere, has tangled with the FTC or the Department of Justice over competition matters at least nine times in the last four years. In four out of five cases, the DOJ derailed a deal or brought an enforcement action. The FTC cleared Google in a majority of its investigations. Here's a look at some of the company's biggest hurdles. (NB: Dates indicate when the investigation closed or action related to the investigation took place.)
DoubleClick acquisition, Dec. 2007
After an 8-month investigation, the FTC cleared Google's $3.2 billion acquisition of digital advertising company DoubleClick. One commissioner dissented, saying the deal could "substantially lessen competition" in the online advertising market.
Yahoo advertising partnership, Nov. 2008
Google abandoned a sweeping advertising agreement with rival Yahoo after the DOJ threatened to sue to block the deal. The deal, which would have brought Google ads to Yahoo's search results, would have "denied consumers the benefits of competition," the DOJ said.
Apple interlocking boards, Aug. 2009
Then Google chief executive Eric Schmidt resigned from the board of Apple amid an FTC investigation into whether the close ties between the two companies could lessen competition. The companies declined to say whether the FTC's antitrust investigation played a role in Schmidt's resignation. Two months later, Arthur Levinson, then chairman of Genentech and a member of Apple's board, resigned from Google's board.
Google books deal, Sep. 2009
The DOJ asked a federal court to block a landmark settlement between Google, the Authors Guild and the Association of American Publishers because of antitrust and copyright concerns. The deal, which would have settled litigation over Google's plan to digitize books from major libraries, would have given the company "de facto exclusive rights for the digital distribution" of millions of books, the DOJ said. In March 2011, the federal court rejected the $125 million settlement, citing opposition from the DOJ and others.
AdMob acquisition, May 2010
After an intensive six-month review, the FTC cleared Google's $750 acquisition million of AdMob, a mobile advertising specialist. The agency said the deal raised "serious antitrust issues" but that it decided not to block it after Apple acquired Quattro Wireless, an AdMob rival.
Hiring practices, Sep. 2010
Six tech giants, including Google, Apple and Intel, settled a DOJ antitrust investigation by ending agreements not to poach each other's employees. The agreements by the companies not to make recruiting calls to employees that they had placed on a list "diminished competition," the DOJ said, and had a negative effect on the job prospects of sought-after engineers and scientists. Adobe, Intuit and Pixar were also part of the settlement.
ITA acquisition, Apr. 2011
The DOJ cleared Google's $700 million acquisition of ITA, a maker of flight search software, but only after Google signed a consent decree limiting how it could use ITA's technology. The settlement forces Google to continue to license ITA's software to rivals and to establish safeguards so it cannot see sensitive information belonging to its competitors.
AdMeld acquisition, Dec. 2011
The DOJ cleared Google's $400 million acquisition of AdMeld, a digital advertising company.
Search, ads and patents, Jan. 2013
The FTC ended its investigation saying Google's search business does not violate antitrust laws. Google agreed to give advertisers more control over their online ad campaigns. In a separate consent decree, Google agreed to license certain patents it obtained through its acquisition of Motorola Mobility under "fair and reasonable" terms.