2019 merger of CBS and Viacom

The 2019 merger of CBS and Viacom was announced on August 13, 2019 and was completed on December 4, 2019. The merger reunited CBS and Viacom into a single company known as ViacomCBS after their separation in January 2006.

Background
The first incarnation of Viacom was created in 1952 as the television syndication division of CBS; it was spun off in 1971. In 1999, Viacom acquired its former parent, then named CBS Corporation (formerly Westinghouse Electric). In January 2006, Viacom was spun off into two entities, CBS Corporation and the second incarnation of Viacom.

September 2016–August 2019
On September 29, 2016, National Amusements sent a letter to Viacom and CBS Corporation, encouraging the two companies to merge back into one company. On December 12, the deal was called off.

On January 12, 2018, CNBC reported that Viacom had re-entered talks to merge back into CBS Corporation, after the merger of AT&T-Time Warner and Disney's acquisition of 21st Century Fox assets were announced. Viacom and CBS also faced heavy competition from companies such as Netflix and Amazon. Shortly afterward, it was reported that the combined company could be a suitor for acquiring the film studio Lionsgate. Viacom and Lionsgate were both interested in acquiring The Weinstein Company. Following the Weinstein effect, Viacom was listed as one of 22 potential buyers that were interested in acquiring The Weinstein Company. They lost the bid, and on March 1, 2018, it was announced that Maria Contreras-Sweet would acquire all of TWC's assets for $500 million.

On March 30, 2018, CBS made an all-stock offer slightly below Viacom's market value, insisting that its existing leadership, including long-time chairman and CEO Les Moonves, oversee the re-combined company. Viacom rejected the offer as too low, requesting a $2.8 billion increase and that Robert Bakish be maintained as president and COO under Moonves. These conflicts had resulted from Shari Redstone seeking more control over CBS and its leadership.

Eventually, on May 14, 2018, CBS Corporation sued its and Viacom's parent company National Amusements and accused Shari Redstone of abusing her voting power in the company and forcing a merger that was not supported by it or Viacom. CBS also accused Redstone of discouraging Verizon Communications from acquiring it, which could have been beneficial to its shareholders.

On May 23, 2018, Les Moonves stated that he considered the Viacom channels to be an "albatross," and while he favors more content for CBS All Access, he believes that there are better deals for CBS than the Viacom deal, such as Metro-Goldwyn-Mayer, Lionsgate or Sony Pictures. Moonves also considered Bakish a threat because he does not want an ally of Shari Redstone as a board member of the combined company.

On September 9, 2018, Les Moonves exited CBS following multiple accusations of sexual assault. National Amusements agreed to make no proposal of a CBS-Viacom merger for at least two years after the date of the settlement.

On May 30, 2019, CNBC reported that CBS Corporation and Viacom would explore merger discussions in mid-June 2019. CBS's board of directors was revamped with people who were open to merging; the re-merger was made possible with the resignation of Moonves, who had opposed all merger attempts. The talks had started following rumors of CBS acquiring Starz from Lionsgate. Reports said that CBS and Viacom reportedly set August 8 as an informal deadline for reaching an agreement to recombine the two media companies. CBS announced to acquire Viacom as part of the re-merger deal for up to $15.4 billion.

On August 2, 2019, it was reported that CBS and Viacom agreed to merge back into one entity. Both companies came to an agreement on the management team for the merger, with Robert Bakish serving as CEO of the combined company with president and acting CEO of CBS, Joseph Ianniello, overseeing CBS-branded assets. On August 7, 2019, CBS and Viacom separately reported their quarterly earnings as the talks about the re-merger continued.

On August 13, CBS and Viacom officially announced their merger; the combined company will be named ViacomCBS. Shari Redstone will also serve as chairwoman of the new company.

August 2019–December 2019
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. The merger must be approved by the Federal Trade Commission.

On October 28, the merger was approved by National Amusements, which then announced the deal would close in early December; the recombined company will trade its shares on NASDAQ under the symbols "VIAC" and "VIACA" after CBS Corporation delist its shares on the New York Stock Exchange.

On November 25, Viacom and CBS have announced to close their merger on December 4 and will begin trading NASDAQ on December 5. The merger has officially closed as of December 4th 2019.