Google Inc. (NASDAQ: GOOG) announced it will acquire online advertising network DoubleClick Inc. for $3.1 billion. The purchase will strengthen Google’s position in the Internet advertising market. It is also the biggest purchase in Google’s history, happening six months after the $1.65 billion YouTube deal.

Microsoft Corp. (NASDAQ: MSFT) was involved in the bidding too, but they backed out after the auction price was higher than $2 billion.

With its more than 1,500 corporate clients, DoubleClick should help Google expand into the markets of print, radio and TV advertising and it should help provide better ad targeting.