Facebook will buy mobile messaging company WhatsApp in a US$19 billion (A$21 billion) deal, the companies announced today.
Facebook said it would pay US$4 billion in cash and about US$12 billion in stock.
The deal also includes US$3 billion in restricted stock units to be granted to WhatsApp staff, that will vest over four years.
The deal equates to around US$42 per each of WhatsApp's 450 million monthly users. Facebook said in a statement WhatsApp added 1 million new users each day.
"WhatsApp is on a path to connect 1 billion people. The services that reach that milestone are all incredibly valuable," Facebook CEO Mark Zuckerberg said in a statement.
"I've known Jan for a long time and I'm excited to partner with him and his team to make the world more open and connected."
Facebook's own Messenger application will operate separately to the WhatsApp product, the company said.
WhatsApp co-founder and CEO Jan Koum will join Facebook's board.