(written from a Production point of view)
The CBS Television Network is the over-the-air main channel family of CBS Television Distribution in the United States. Originally launched in 1941 as the Columbia Broadcasting System, CBS was one of the four early broadcast television networks in America, along with NBC, ABC, and the now-defunct DuMont Network.
Over the 80 year history of the network, some of the most popular programs have included The Dick Van Dyke Show, M*A*S*H, The Andy Griffith Show, All in the Family, The Carol Burnett Show, and more recently, Everybody Loves Raymond, The Big Bang Theory, and the NCIS franchise.
One of the earliest hit series on CBS was I Love Lucy, produced by Desilu from 1951-1957. In 1964, after Gene Roddenberry signed a three-year contract with Desilu, CBS was offered the Star Trek: The Original Series pitch, but ultimately rejected it in favor of the more accessible "family" show Lost in Space. Roddenberry, of course, would end up selling the series to competing network NBC. (The Making of Star Trek; Inside Star Trek: The Real Story) Ironically, CBS Corporation acquired the Star Trek franchise in 2006 after a series of mergers, but did not commission any new Star Trek series until 2015.
On 24 September 2017, the first episode of Star Trek: Discovery, "The Vulcan Hello", premiered on the channel before the remainder of the series was broadcast on CBS All Access. The channel rebroadcasted this episode on 24 September 2020, exactly three years after its first airing and is following up with a broadcast of the entire first season of Discovery, previously made available on CBS All Access.