The world’s largest social network has purchased a popular mobile photo sharing app for a whopping $1 billion. And just a few years ago, no one had even heard of Facebook or Instagram.

“We've agreed to acquire Instagram, and their talented team will be joining Facebook,” Facebook Cofounder and CEO Mark Zuckerberg wrote in a post on his own service. “We'll work even more closely with the Instagram team to also offer the best experiences for sharing beautiful mobile photos with people based on your interests.”

For those not familiar, Instagram is a photo-sharing app for iPhone and Android handsets. It’s unclear why the app is so popular, as it transforms modern, smartphone photos into old-fashioned shots using filters designed to emulate Polaroid and other vintage cameras. Instagram doesn’t even host its own online service: Sharing occurs through third-party services such as Facebook, Twitter, and Tumblr.

Of course, Facebook has quickly become one of the most popular ways to share photos online and is expected to soon surpass legacy services like Flickr. So it’s no wonder that it would seek to bolster its photo-sharing capabilities.

That said, Facebook intends to keep Instagram a separate business and continue developing the mobile apps so that they can share on other social networks too. “Instagram is not going away,” Instagram CEO Kevin Systrom noted on the Instagram blog. “We’ll continue to add new features to the product and find new ways to create a better mobile photos experience.”