Mark Zuckerberg made a rare public post to his Facebook page today to announce that his company is spending $1 billion to buy Instagram, a social network used to share photos taken with phones and modified with retro filters.

Zuckerberg wrote that Instagram would continue to operate “independently.” Users will be able to keep their Instagram photos, friends, and followers separate from their Facebook account, he said. At the same time, Facebook will get features similar to those of Instagram. The acquisition is Facebook’s largest, and suggests the company is willing to spend large amounts to ensure it retains its status as the most dominant social network.