Facebook has officially bought Microsoft's Atlas advertising platform. In a statement, the company said Atlas would give advertisers a better idea of how their campaigns were doing and would "help advertisers compare their Facebook campaigns to the rest of their ad spending across the web on desktop and mobile." Atlas, Facebook says, is already in use by many advertisers on the site, but the company is planning to build out both its measurement systems and its user interface, making it easier to use and offering a more complete picture of campaigns. As Facebook works to monetize its system, this will become particularly important — despite fast growth, it's been hard to find good metrics on how well its ads actually work.

Though Facebook doesn't mention it, owning an ad serving platform could also let it provide ads on sites outside its own, making it a competitor to Google and its AdSense platform. The Facebook and Microsoft deal was previously rumored in December, and we're still not sure how much Facebook paid for the service. AdAge suggested previously that it was expected to sell for less than $100 million; Microsoft originally acquired aQuantive, which provided the technology, for around $6 billion.

Update: Microsoft has also explained its reasons behind the deal. In an email, advertising communications director Tom Phillips said selling Atlas was part of its move to a greater focus on the "devices and services model." It also downplayed the importance of ad serving altogether, saying that "digital advertising today is not fulfilling its promise. Consumers really don’t want ads per se — they want digital content and experiences that enhance what they’re doing, whether that comes from brands, publishers or peers."