CBS Radio Mystery Theater (a.k.a. Radio Mystery Theater and Mystery Theater, sometimes abbreviated as CBSRMT) is a radio drama series created by Himan Brown that was broadcast on CBS Radio Network affiliates from 1974 to 1982, and later in the early 2000s was repeated by the NPR satellite feed.The format was similar to that of classic old time radio shows like The Mysterious Traveler and The Whistler, in that the episodes were introduced by host E. G. Marshall who provided pithy wisdom and commentary throughout.

Unlike the hosts of those earlier programs, Marshall is fully mortal, merely someone whose heightened insight and erudition plunge the listener into the world of the macabre.As with Himan Brown's prior Inner Sanctum Mysteries, each episode of CBS Radio Mystery Theater opened and closed with the ominous sound of a creaking door. This sound effect is accompanied by Marshall's greeting, "Come in!… Welcome. I'm E. G. Marshall."

At each show's conclusion, the door swings shut, and Marshall signs off with: "Until next time, pleasant… dreams?" This is followed by an extended variation of the show's theme music.CBSRMT was broadcast each weeknight, at first with a new program each night. Later in the run, three or four episodes were new originals each week, and the remainder repeats. There were 1,399 original episodes. The total number of broadcasts, including repeats, was 2,969.