On December 31, 2005, American mass media company Viacom split into two companies: the second CBS Corporation, its successor (the first being a short lived rename of Westinghouse Electric) which held the namesake flagship channel CBS, CBS News, CBS Sports, Showtime Networks, UPN (merged with The WB to form the CW, co-owned by Time Warner), Smithsonian Channel, Simon and Schuster, Infinity Broadcasting Corporation, Viacom Outdoor, and Paramount Television, and an entirely new Viacom which held Paramount Pictures, Nickelodeon, Nick Jr., Noggin, Nicktoons, TEENick, Music Television, Black Entertainment Television, Video Hits One, Country Music Television, and later DreamWorks, respectively.

In March 2005, Viacom contemplated splitting the company into two publicly traded companies, amid issues of the stock price stagnating and clashing corporate cultures between the cable and broadcast divisions, which came to a head with the Super Bowl XXXVIII halftime show controversy a year previous with the MTV-produced show causing controversy for game broadcaster CBS.

CBS said: "In many ways, today's decision is a natural extension of the path we laid out in creating Viacom," Redstone said in a company-wide memo.

"We are retaining the significant advantages we captured in the Paramount and CBS mergers and, at the same time, recognizing the need to adapt to a changing competitive environment.

On August 13, 2019, CBS and Viacom officially announced their merger; the combined company was to be named ViacomCBS, with Shari Redstone serving as chair.

[11][12][13] Upon the merger agreement, Viacom and CBS jointly announced that the transaction is expected to close by the end of 2019, pending regulatory and shareholder approvals.