According to Robert H. Justman in his book "Star Trek: The Real Story", this show's famous theme was not the first one written. Lalo Schifrin had written a main theme, but creator and executive producer Bruce Geller decided that it was inappropriate. Instead, Geller used some chase music Schifrin had written for the end of the first episode. That throwaway musical cue became one of the most famous and recognizable television show themes in history.
The main reason for Briggs, and later Phelps, looking through the photos to select the various members of the team for each mission was that many of the early episodes would feature guest stars as members of the team. However, once it became apparent that the same members were chosen every time, the practice was eventually abandoned.
The faceless figure shown striking a match in the opening credits is Bruce Geller himself. It wasn't until the 1988 revival of the series that an established character (Jim Phelps) was shown lighting it.
The character played by Lynda Day George during Seasons Six and Seven is now credited as "Lisa Casey." That name only came about as a result of the 1988-1990 revival series, however. When George was brought back in 1989 in Episode 17 of the revival (titled "Reprisal") to play the same character she had played during the original, the creators were concerned that there might be some confusion between her character and the one played earlier during the revival series by Terry Markwell, who had also been named "Casey." Even though Markwell's character had been killed off in Episode 12 of that season ("The Fortune"), they abruptly re-christened the original Casey as "Lisa Casey" - a name George's character had never used in any of her 41 appearances during the original run of the series.
During the first season, Martin Landau's face was not shown during the main title sequence. In fact, during that season he was credited as making a "special appearance". It wasn't until season two that he was acknowledged as being a full cast member. This was because Landau, who at the time had a thriving motion picture career, didn't want to commit himself to the standard five-year contract that studios typically required of actors in a television series. Series producer Bruce Geller wanted Landau badly enough, however, that he agreed to use him on a "guest star" basis during the first season; Landau signed one-year contracts at the beginning of the second and third seasons.
Nearly every non-lead actor or actress that worked on "Star Trek" also appears in "Mission:Impossible". This is probably due to both shows filming at the Desilu Studios. Lead "Star Trek" performers, also guest appearing, include George Takei, William Shatner, and eventual series regular Leonard Nimoy.
Even though Rollin, Cinnamon, Paris and Willie were somewhat famous for their various professions outside of their work with the IMF, no one ever recognized them during any IMF missions, even the ones they undertook within the United States.
For several years the series first season was not shown in syndication due to the fact that many people had grown so accustomed to Jim Phelps (Peter Graves) being the leader of the team that many viewers were shocked when they saw the first season reruns with Dan Briggs (Steven Hill) as the leader of the IMF.
In numerous episodes a large, white, ornate archway with a metal gate was used, usually as the entrance to a prison. This was, in reality, the old main gate at Paramount studios where the series was filmed.
When the reel-to-reel tape recorder is playing the mission's instructions, it is actually in a "rewind" mode rather than a "play" mode. This was done because the tape moved too slowly to be believed when it was "playing".
The episodes "Action", "The Town" and "Kidnap" are the only ones in which the head of the IMF team did not receive instructions. In "Action", Cinnamon Carter (Barbara Bain) received the instructions instead. It's also the only episode in the first season in which Dan Briggs (Steven Hill) did not appear. In "The Town", Phelps is on vacation when he uncovers a town of assassins who immobilize & try to kill him. In "Kidnap" Phelps is kidnapped and the information for his release is given to Barney (Greg Morris). There are only six episodes that are not "true missions". They include two of the above ("The Town" and "Kidnap") as well as "Death Squad" where Barney is charged with murder, "The Condemned" where Phelps has to help a friend who has been charged with murder and "The Ransom" where Briggs has to save a friend's kidnapped daughter. In "Cat's Paw" Barney's brother is murdered and the team helps him bring those responsible to justice.
When Dan (Steven Hill) or Jim (Peter Graves) received instructions, the usual last words were "This tape will self-destruct in 5 seconds". However, the other instruction they would receive was "Please dispose of this tape by the usual means", whereby they would throw the tape into an incinerator or toss it into a vat of acid.
Lalo Schifrin's score - played in a highly uncommon 5/4 time signature earlier popularized by Dave Brubeck's "Take Five" (1959) - went on to achieve the dubious distinction of most parodied theme music closely paralleled by the Twilight Zone (1959)'s eerie leitmotif trill.
Only 120 missions include the famous warning that the tape will "self-destruct". Five say that the tape will "decompose", one says that it will "destroy itself", twelve instruct Briggs or Phelps to "dispose of" the recording, seven tell them to "destroy" it, and three contain no instructions, but Phelps destroys the recording anyway. The remaining fifteen missions contain no recorded briefing at all.
The show reused many stars in different roles as different people. For example: John Vernon appeared as Colonel Josef Strom ("The Exchange"), General Ramon Sabattini ("The Falcon"), Ramone Fuego ("The Catafalque") and Norman Shields ("Movie"). William Windom appeared as Paul Mitchell ("The Fighter"), Stu Gorman ("Blues"), Alex Cresnic ("The Widow") and Deputy Premier Milos Pavel ("The Train"). This was a common practice on long running TV shows in the 1960s.
This series gave Peter Lupus, who played Willy, the chance to work under his own name. Most of his previous acting career was in Europe where he played the lead role in sword and sandal/mythological muscleman movies under the name "Rock Stevens". This also gave him a chance to act in a role that didn't rely mainly on his physique.
Although the IMF usually received its instructions from a self-destructing reel-to-reel tape, this didn't become the norm until several seasons into the series. In early episodes, Briggs and Phelps got their instructions from other sources such as records and filmstrip projectors. The "tape scenes" for each episode (as they were known) were usually filmed in one block at the start of each season. Peter Graves said he never knew which episode would use which tape scene until it was broadcast.
When this show was bought by ARD for the West German market in 1967, only selected episodes from the first three seasons were dubbed (additionally the episodes were cut down to standard running time of 45 minutes). A few years later they did the same with the later seasons (with new dubbing actors). When the show was broadcast on Kabel 1/Pro 7, all other episodes (except one) were dubbed as well (again with new dubbing actors). The last remaining episode was dubbed for the DVD release in 2006.