Facebook has announced a partnership with Skype to add video chat to the social networking site.
The move is likely to be seen as a shot across the bow of Google, which recently launched a Facebook rival, Google+, also featuring video calling.
This is not the first time Facebook and Skype have teamed up - they already share some instant messaging tools.
Skype is in the process of being bought by Microsoft, which is a major shareholder in Facebook.
The new video-call service was launched by Facebook founder Mark Zuckerberg, who also revealed that the site now had more than 750 million users.
However, he said that the total number of active users was no longer a useful measure of the site's success.
Instead, the amount of sharing - of photographs, videos and web links - was a better indication of how people engaged with the site, explained Mr Zuckerberg.
One to one
At launch, Facebook's video chat service will only be able to connect two users face-to-face, whereas Google's system allows group video calls, known as Hangouts.
Mr Zuckerberg said that it was likely that other "premium" Skype functions would be added in future.
He also appeared to offer a back-handed compliment to Google+, saying that its creation was a vindication of Facebook's vision for the social web.
Industry analysts welcomed the announcement.
"Advertisers love anything that keeps users on Facebook for longer and that is something Facebook has been brilliant at - keeping people engaged with the platform for increasingly longer periods of time," Susan Etlinger of the Altimeter Group told BBC News.
"It stands to reason that the longer you are on Facebook, the happier advertisers will be."
In California, Skype chief executive Tony Bates welcomed the partnership, calling it a "long-term relationship" that could benefit both companies.
At one point he had to correct Mr Zuckerberg on the subject of Skype's ownership, reminding him that the Microsoft deal was not yet complete and still had to be cleared by regulators.
The tie-in was announced a week after Google announced its own social networking service, Google+.
"The two companies built these products separately and independently over a number of months but they will be compared directly," said Ben Parr, editor-at-large of social media blog Mashable.com.
"They are going to be in more heated competition in the next year or so and you are going to hear a lot about who is going to win the social networking war - how does Google catch up, how does Facebook respond. This story isn't going away."