Insanely popular photo app and social network Instagram has been acquired by Facebook for approximately $1 billion in a combination of cash and shares. The service will remain running as it is for now, and CEO Kevin Systrom says that it’s “not going away.”

Facebook’s Mark Zuckerberg says the company has agreed to acquire Instagram and that they will be “able to 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.”

Systrom goes on to say that they’ve had an ‘amazing time’ watching Instagram grow and that “with the support and cross-pollination of ideas and talent at a place like Facebook, we hope to create an even more exciting future for Instagram and Facebook alike.”

He also says that it’s important to be clear that the service “is not going away” and that the company will be working with Facebook to evolve the service and build the network. He says that you will also continue to be able to share to other social networks, presumably including Twitter, and that the app will keep all of its features.

Zuckerberg says that Facebook will be working closely with the Instagram team to help you enjoy “beautiful mobile photos with people based on your interests.”

He also says that Facebook will be keeping and building on Instagram’s strengths, rather than just absorbing its features into Facebook. To that end, Instagram will stay independent from Facebook. The company wants to spread the app and ‘brand’ to more people. He also reaffirms that Instagram will retain the ability to post to other networks, not just share photos on Facebook and to keep your followers and following lists separate as well. “At the same time,” he continues, “we will try to help Instagram continue to grow by using Facebook’s strong engineering team and infrastructure.”

“This is an important milestone for Facebook because it’s the first time we’ve ever acquired a product and company with so many users,” Zuckerberg says. “We don’t plan on doing many more of these, if any at all. But providing the best photo sharing experience is one reason why so many people love Facebook and we knew it would be worth bringing these two companies together.”

On Tuesday, Instagram released its photo sharing client on Android. It racked up a million downloads in a day and we found it to compare well to its iOS counterpart. Instagram also wrote its own push notification server for the Android app, and it is offering it up as open-source.

This intent to acquire means that it took roughly 551 days from Instagram’s launch to its sale for $1Bn. This is incredible growth for a tiny company that only has 11 employees. The transaction will go through some time later this year and makes the deal worth roughly $33 per Instagram user.