The European regulators were the last potential obstacle to the deal after it was approved by the US Department of Justice in December 2007.
The EU said there was no evidence that Google/DoubleClick could marginalise competitors, because they all provided "credible" alternatives for online ads.
Opponents to the deal included Microsoft, Yahoo, advertisers and privacy advocates, who all claimed the deal would allow Google to dominate the online advertising market.
DoubleClick, who are based in New York, provides a service to help its customers place and track advertising on websites.
They are one of the biggest players in their field. By installing small bits of software, or "cookies", onto users' computers, they can track the pages that are viewed, allowing ads to be targetted to browsing habits.
This includes search ads, which targets adverts on web pages that customers are likely to use, generating money for themselves and the smaller publishers and lesser-visited sites that deploy them.
Google has turned this into a lucrative business, outstripping its nearest search compteitors Yahoo and Microsoft.
Personal privacy
In it's decision, the European Commission said that Google and DoubleClick are not rivals and that Google's purchase of even a potential competitor would not have an adverse impact on competition.
"The transaction would be unlikely to have harmful effects on consumers," the report said.
They also said their decision was based solely on the economic aspects of the acquisition, and that it had no bearing on Google's obligations under EU regulations covering protection of personal privacy or how personal data in stored and processed.
Privacy advocates feared that by merging their databases on people's internet activities, this would have a serious implications for data protection.
European data privacy regulators have begun an investigation into how the policies of search engine operators like Google and Yahoo comply with existing EU laws.
Their report is due in April, but officials have already indicated that the rules would apply to companies based outside Europe.