Facebook is buying the fast-growing mobile messaging service WhatsApp for more than $19 billion in cash and stock, expanding the global footprint of the social networking giant.
The deal bolsters the world's biggest social network by adding the 450 million users of WhatsApp, which will be operated independently with its own board.
It is Facebook's biggest acquisition and comes less than two years after Mark Zuckerberg's firm raised $16bn in the richest tech sector public stock offering.
The purchase includes $12bn in Facebook shares and $4bn cash.
It calls for an additional $3bn in restricted stock units to be granted to WhatsApp founders and employees that will vest over four years.
"The acquisition supports Facebook and WhatsApp's shared mission to bring more connectivity and utility to the world by delivering core Internet services efficiently and affordably," Facebook said.
Facebook reportedly sought to acquire another messaging firm, Snapchat, for $3bn last year.
"WhatsApp is on a path to connect one billion people. The services that reach that milestone are all incredibly valuable," said Mr Zuckerberg.
"I've known (WhatsApp founder) Jan (Koum) for a long time and I'm excited to partner with him and his team to make the world more open and connected."
WhatsApp is a cross-platform mobile app that allows users to exchange messages without having to pay telecom charges.
"Almost five years ago we started WhatsApp with a simple mission: building a cool product used globally by everybody. Nothing else mattered to us," Mr Koum said in a blog post.
"Today we are announcing a partnership with Facebook that will allow us to continue on that simple mission.
"Doing this will give WhatsApp the flexibility to grow and expand, while giving me, (co-founder) Brian (Acton), and the rest of our team more time to focus on building a communications service that's as fast, affordable and personal as possible."