(written from a Production point of view)
CBS Studios, officially known as CBS Broadcasting, Inc. and better known simply as CBS (Columbia Broadcasting System), is the television broadcasting network which currently owns the trademarks of Star Trek and all related marks.
CBS's first involvement with Star Trek actually occurred in 1964, during Gene Roddenberry's attempt to sell "The Cage" to a television network. CBS was the first outlet to which Roddenberry offered Star Trek, but CBS declined. The show ultimately went to NBC.
CBS Studios were previously under the ownership by the media conglomerate Viacom until that company split into two separate publicly traded companies: CBS Corporation and a new Viacom. CBS Studios now falls under the ownership of the CBS Corporation.