(written from a Production point of view)
CBS Studios, officially known as CBS Broadcasting, Inc. and better known simply as CBS (formerly the Columbia Broadcasting System), is the television broadcasting network whose current holding company, CBS Corporation, owns the trademarks of Star Trek and all related marks.
CBS's first involvement with Star Trek actually occurred in late April 1964, during Gene Roddenberry's attempt to sell "The Cage" to a television network. On that occassion he was accompanied by Desilu executive Oscar Katz. CBS was, after MGM the previous month, the second outlet to which Roddenberry offered Star Trek, but CBS declined, but not after both men – Roddenberry in particular – were thoroughly grilled on the offered property. As it turned out, CBS had its own science fiction show, Lost in Space, under development at that time and never had any intention to add a second science fiction show to their line-up. Both Katz and Roddenberry specifically were convinced that CBS had picked their brains, after they had become aware of that fact. (Star Trek Creator: The Authorized Biography of Gene Roddenberry) The show ultimately went to NBC.
When the original CBS Studios came under the ownership by the media conglomerate Viacom in 2000, it was on that occasion restructured and merged with Paramount Studios's television division (itself a 1967 merged version of Paramount's hitherto insignificant television division and Desilu Studios) and rechristened "CBS Paramount Television".
In late 2005 the original Viacom conglomerate was spun off into two separate publicly traded companies: CBS Corporation and a new Viacom with the television division presently falling under the ownership of the CBS Corporation. On that occassion the former television division was split into two subsidiaries as well, the present broadcast television network "CBS" – essentially the original CBS Studios, and thus, in a manner of speaking, coming full circle – and the television production company currently known under its latest iteration "CBS Television Studios". The licensing of consumer products related to Star Trek is presently controlled by the CBS Consumer Products sister division.