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 I.M.F.

Greg Morris and Peter Lupus were the only original cast members to remain on the show throughout the entire run, although Lupus was replaced by Sam Elliott for approximately half of the episodes in season five.

Steven Hill left the cast after one season for two main reasons: because as an Orthodox Jew, and being unwilling to abide by the show's production schedule that would have required him to work on the Sabbath; and his disruptive behavior, often causing filming to shut down.

Only one hundred twenty 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 Daniel Briggs (Steven Hill) or Jim Phelps (Peter Graves) to "dispose of" the recording, seven tell them to "destroy" it, and three contain no instructions, but Jim destroys the recordings anyway.

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.

Nearly every non-lead actor or actress that worked on "Star Trek" (1966) also appeared on this show. This is probably due to both shows having been filmed at "Desilu Studios." Lead "Star Trek" (1966) performers, also guest appearing, include George Takei, William Shatner, and eventual series regular Leonard Nimoy.

The main reason for Daniel Briggs (Steven Hill), and later Jim Phelps (Peter Graves), 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 was Series Creator Bruce Geller. It wasn't until the 1988 revival of the series that an established character (Jim Phelps) was shown lighting it.

This show (not including the 1988 sequel series) had the most episodes of any English-language spy series, with one hundred seventy-one episodes. Its nearest rival is "The Avengers (1961)," with one hundred sixty-one episodes.

During the fifth season, Willy (Peter Lupus) was replaced in some episodes by Doug (Sam Elliott).

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 Pictures Studios, where the series was filmed.

When the reel-to-reel tape recorder was playing the mission's instructions, it was 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".

During the first season, Martin Landau's face was not shown during the main title sequence. 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 and actresses 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.

Martin Landau and his then wife Barbara Bain jointly left the show after the third season, due to a contract dispute after their demands for a salary raise weren't met.

Cancelled in 1973, it was the last survivor of the 1960s spy series craze that had produced shows like The Man from U.N.C.L.E. (1964), Secret Agent (1964), Get Smart (1965), The Wild Wild West (1965), et cetera.

Season one, episode twenty-three, "Action!"; season two, episode twenty-one, "The Town"; and season seven, episode eleven, "Kidnap" are the only ones in which the head of the I.M.F. 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 Daniel Briggs (Steven Hill) did not appear. In "The Town", Jim Phelps (Peter Graves) was on vacation when he uncovered a town of assassins who immobilize and try to kill him. In "Kidnap", Phelps was kidnapped and the information for his release was given to Barney Collier (Greg Morris). In season five, episode four, "Homecoming", Jim arrived in his hometown to discover someone was killing the young women. There are only six episodes that are not "true missions". They include two of the above ("Homecoming" and "Kidnap") as well as season four, episode twenty-four, "Death Squad", where Barney was charged with murder; season two, episode nineteen, "The Condemned", where Phelps had to help a friend who had been charged with murder; and season one, episode eight, "The Ransom", where Briggs had to save a friend's kidnapped daughter. In season five, episode fifteen, "Cat's Paw", Barney's brother was murdered, and the team helped him bring those responsible to justice.

When selecting Agents from the I.M.F. folder, the pictures of the Agents selected for the mission were almost always in color. Rejected Agents' pictures were in black-and-white.

Television shows of the era that filmed at the same studios often shared minor cast members. It is common to see familiar faces on episodes of "Star Trek: The Original Series (1966)," "Batman (1966)," this show, and "The Wild Wild West (1965)."

Although the I.M.F. usually received its instructions from a self-destructing reel-to-reel tape, the first two seasons often featured other methods. 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.

In season one, episode two, "Memory", Briggs did not receive his instructions via tape or filmstrip projector, but on a card handed to him by a photographer.

This series gave Peter Lupus (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.

In season five, the producers wanted to replace Peter Lupus with Sam Elliott, apparently because they thought Lupus was s bad actor. However, the show's fans were so upset with the decision, that Peter Lupus was kept on, with Sam Elliott appearing in approximately six episodes in season five, and one episode in season six.

Leonard Nimoy's Paris character replaced Martin Landau's Rollin Hand character in season four. It's believed that largely because of this, the fact that Landau was originally offered Nimoy's famous Spock character in Star Trek: The Original Series (1966) became widespread.

After five seasons of stories of international intrigue, the I.M.F. spent the final two seasons going after American gangsters.

As of November 2019, Peter Lupus and Sam Elliott are the only surviving male regular cast members.

The fourth season was the only one not to feature a regular female cast member.

The show re-used many actors and actresses 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 television shows in the 1960s.

When Lynda Day George was forced to miss several episodes during the seventh season, due to maternity leave, her absence was explained by having Casey on a "special assignment" in Europe for the I.M.F.

The only one of the team shown to have a relative was Barney Collier, whose brother, Lawrence was murdered in season five, episode fifteen, "Cat's Paw".

The campus of the California Institute of Technology in Pasadena, California was often used as a backdrop for episodes located in foreign countries.

Many episodes involve warehouses and industrial buildings. These were office buildings, warehouses and soundstages on the Paramount lot.

Television Producer Bernard L. Kowalski, who'd been immensely impressed by the general mood and style of "The Ipcress File (1965)," requested that a similar ambiance and urgency be emulated for this show.

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 Mission: Impossible (1988), however. When George was brought back in season one, episode seventeen, "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 by Terry Markwell, who had also been named "Casey". Even though Markwell's character had been killed off in season one, episode twelve, "The Fortune", they abruptly re-christened the original Casey as "Lisa Casey", a name George's character had never used in any of her forty-one appearances during the original run of the series.

Despite the I.M.F. being a secret organization, many of the team members had a very high public profile. They are featured on magazine covers: Cinnamon Carter (Barbara Bain) was "model of the year", Rollin Hand (Martin Landau) was a well-known actor, Barney Collier (Greg Morris) was founder/owner/President of an electronics firm, and Willy Armitage (Peter Lupus) was a record-setting weightlifter.

Of the one hundred forty-eight missions in which Phelps or Briggs received a tape recorded briefing, one hundred nineteen began with "Good morning", twenty-one with "Good afternoon", and eight with "Good evening".

Because of the disguises he wore, Rollin Hand (Martin Landau) was known as "The Man of a Million Faces".

There never was any explanation given for why Daniel Briggs was no longer the head of the I.M.F., and how Jim Phelps became the head of the team.

When Dan (Steven Hill) or Jim (Peter Graves) received instructions, the usual last words were "This tape will self-destruct in five 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 The Twilight Zone (1959)'s eerie leitmotif trill.

Pasadena City Hall in Pasadena, California was often used as a foreign country's capital building.

Greg Morris appeared in the most episodes of the series, he was absent for just five. He is also the only cast member who appeared in all one hundred seventy-one opening credits.

In the first season, Steven Hill (Daniel Briggs) can be seen driving either a black or light blue 1967 Lincoln Continental convertible.

In six season one episodes, Daniel Briggs (Steven Hill) is seen receiving his instructions and setting up the missions, but does not go on the mission. These are episode six, "Odds on Evil"; episode eleven, "Zubrovnik's Ghost"; episode thirteen, "Elena"; episode sixteen, "The Reluctant Dragon"; episode twenty-four, "The Train"; and episode twenty-eight, "The Psychic".

In season one, episode three, "Operation Rogosh", when Briggs is choosing Agents for the mission, the last photo left in the portfolio is of Series Creator Bruce Geller.

It become apparent from binge watching the series, that not only did they re-use existing exterior standing sets and buildings on the former "R.K.O./Desilu/Paramount" lots, with minor to major set dressing, but also certain huge interior studios sets - example in season two, the massive hotel lobby rooms re-appear dressed as the King's palace rooms. The basement cells with distinct walls become a Palace dungeon, and a South American prison. Unsurprisingly, some of these same standing sets were re-used in Desilu-Paramount's "Star Trek" (1966) as other planet locations.

During season one, Briggs selected the use of a Repertory Theatre/Theater group within the Mission. This episode, "Operation Rogosh", officially establishes that the I.M.F. is a much larger organization, with a much bigger pool of Agents than the series generally focused on. This could now also explain how so many Mission elements are in place, such as building space, vehicles, costumes, et cetera, are in place before the I.M.F. team commence each mission, with more existing Agents already in-situ "on the ground".

Contrary to popular belief, Leonard Nimoy and William Shatner never appeared on the same episode. Nimoy's time of starring on the series was actually in-between Shatner's two episode appearances.

According to Peter Lupus, Series Creator Bruce Geller did not want any of the regular cast members making appearances on talk shows during the run, because he wanted viewers to believe they were actually the characters.

The same footage was used over and over for the beginning sequences. The only thing that was changed was the soundtrack from the tape recorder, and the pictures, at which Phelps looked.

When Lynda Day George went on maternity leave during season seven, the explanation for her character's absence was that she was on special assignment in Europe. This is the only time that the reason for a regular cast member disappearance from the series is mentioned.

In season two, episode fifteen, "The Photographer", it's revealed, or at least it's implied, Cinnamon's full (model) name is Cinnamon Carter Crawford. The photographer already recognizes her from her earlier modelling career. The episode implies that she is, a retired model, and a bio-chemist, as well as her established I.M.F. position. It's already been established with the story-universe that she has some knowledge of a field of medicine, as she is always the default nurse when a mission requires it, and is highly intelligent. If the top secret Government bio-chemist is her actual official employment cover story, it explains how she can be away on so many Missions, and not be as recognized.

Bob Johnson (the voice heard on most episodes saying, "Good morning, Mr Briggs", or "Phelps...") was the only actor besides Greg Morris and Peter Lupus to work for the entire run of the show.

Included amongst the "1001 television shows you must see before you die", edited by Steven Schneider.

When the show began, Ford was the main supplier of cars. During the later seasons, Chrysler was the main supplier, and in the final seasons, it was GM.

When Jim Phelps (Peter Graves} first appeared, his main ride was a greenish-blue 1967 Mercury Parklane convertible.

In nearly every episode, the bulk of the "incidential" music is actually various arrangements of the main theme, played in various styles, instruments, and timings. Apart from the more traditional studio orchestra style, you can also hear regal harpsichords, military drums, pianos, strings, wind, and experimental jazz styles.

In the pilot episode, Cinnamon seems to freely admit and accept that part of her I.M.F. role includes being a distraction as a good-looking woman, when the Mission requires it. As she also is a model that would also suit her selection for certain Missions. Obviously she is also highly intelligent, and is a versatile team member able to play other women, often in disguise, whenever the Missions require it. She is far from being the "token" woman team member, and is an equal to the rest of the I.M.F. team.

The exact Secretary is never disclosed, but, given the I.M.F.'s international purview in the first five seasons, it is almost certainly the Secretary of State. However, given that the Secretary is not mentioned at all in the last two seasons, and that the team's missions deal almost exclusively with organized crime, it is possible that the I.M.F. has been moved from the State Department to the Justice Department. Some fans of the show have assumed that the Secretary refers to the Secretary of the IMF.

Whenever Dan or Jim received their instructions, They always turned on the tape recorder first, then opened the folder with the photographs.

Weapons used dated from World War II, for 1960s-era episodes.

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 forty-five minutes). A few years later, they did the same with the later seasons (with new dubbing actors and actresses). When the show was broadcast on Kabel 1/Pro 7, all other episodes (except one) were dubbed as well (again with new dubbing actors and actresses). The last remaining episode was dubbed for the DVD release in 2006.

Academy Award winners Edmund O'Brien and George Sanders appeared on this show. O'Brien in season two, episode twenty, "The Counterfeiter", and Sanders in season five, episode twenty-three, "The Merchant".

The logical economical production reason for the occasional re-used scenes of Jim receiving the Missions is obvious as it saves mounting pre-title/cold opening shoots. However, within the story universe it can easily be explained as the I.M.F. have a known number of locations Jim goes to several times receive the Missions. For example, in season two, Jim happens to visit both the roof, and the street photo booth twice, for four separate missions. He clearly knows the locations well within the story universe, and in season two, has all the keys he needs.

In a couple of later episodes, Jim Phelps could be seen driving a 1969 Dodge Coronet R/T convertible. This is an extremely rare car.

Whenever someone wore a rubber mask, it was almost always one of the heroes.

Martin Landau and Lesley Ann Warren appeared in Joseph (1995).

Drone was used in season three, episode nineteen, "The Bunker".

Spoofed in Mad Magazine as "Mission: Ridiculous".

The mission assignment recording most often self-destructs after five seconds. Six times it is ten seconds. For the Pilot it is "one minute" after breaking the seal, and another time it is "sixty seconds." Once it is when you stop the machine, and once when it reaches the final groove. Only Miss Carter is told that it will decompose "immediately."

1967 season of "The Avengers" included The Avengers: Mission... Highly Improbable (1967)

Its never explained within the story universe as to the amount of time passing between Jim initially receiving the mission, selecting the team, planning for it, getting the relative material and people in place, running the Mission, and then completing it by the end of the episode.

All mission assignment recordings end in "Good luck, Dan" (season one) or "Good luck, Jim" (seasons two through seven) except the one recording for "Miss Carter" (season one, "Action!") ends in "Good luck."