Entertainment giants CBS and Viacom are to merge in the latest media mega-deal as broadcasters adapt to changing consumer demands.
The new company will have $28bn in revenue and comprise brands like MTV, Comedy Central and Paramount Pictures.
The deal would reunite the two firms, which were previously under the same corporate umbrella until a 2006 split.
The move comes amid an increasingly competitive landscape dominated by Netflix, Disney-Fox and other rivals.
The merged firm, to be called ViacomCBS, would be controlled by National Amusements, the holding company owned by billionaire Sumner Redstone and his daughter, Shari.
There have been at least three attempts to re-combine the companies, but all failed due to clashes between executives and investors over who got the top jobs as well as the valuations of the business.
There was also the dramatic fall of CBS's boss Les Moonves, ousted after allegations of sexual misconduct.
Viacom chief executive Bob Bakish will be the president and chief executive of the combined company. Joe Ianniello, interim chief executive of CBS, will be named chairman and chief of CBS.
The companies said they expected about $500m cost savings from the tie-up, which brings together a movie studio, string of cable channels, and some of US TV's most-watched shows, including 60 Minutes and The Big Bang Theory.
In addition to their US operations, the merged group will have a global reach, including in Britain, Argentina and Australia.
'Content is king'
"I am really excited to see these two great companies come together so that they can realise the incredible power of their combined assets," said Shari Redstone, who will chair the new company, ViacomCBS.
The daughter of Sumner Redstone said: "My father once said 'content is king,' and never has that been more true than today. We will establish a world-class, multiplatform media organisation that is well-positioned for growth in a rapidly transforming industry."
Mr Redstone broke up CBS and Viacom 14 years ago. He believed it would unlock the value of Viacom, which was broadcasting some of TV's most popular shows at a time when CBS was becoming less popular.
Shari Redstone had been a big backer of re-combining the companies in the face of tough competition. The mergers of Disney with Fox, and AT&T and Time Warner, coupled with expanding streaming services, left CBS and Viacom in a weaker position.