When Facebook introduced its ad platform in 2007, advertisers could target people using information they had volunteered on the platform. Three years later, Facebook introduced Custom Audiences, a feature that allowed companies to upload their own lists of people to target. A retailer, for example, could upload its customer list and target ads at those who had recently bought a specific kind of T-shirt. In mid-2014, Facebook incorporated users’ online browsing history into its ad-targeting platform. The company had been collecting browsing data for years, from any web page that included a Facebook like button or had let people log in through their Facebook accounts. Get the full story at The New York Times