CBS Corporation and Viacom have entered into a definitive agreement to combine in an all-stock merger, reuniting two US-based media giants which split in 2006. The merger will reunite the CBS free-to-air broadcasting business, the Showtime pay TV network, basic cable channel brands MTV, Nickelodeon and Comedy Central, and the Paramount film and TV studios, as well as burgeoning online brands including CBS All Access and Pluto TV. Both CBS and Viacom are owned by National Amusements Inc.