At Fred MacMurray's insistence, all episodes were filmed out of sequence during the show's entire run using a technique now known as the MacMurray method. MacMurray would do all of his scenes in 65 nonconsecutive days. The cast regulars got haircuts once a week in order to maintain continuity. Guest stars would have to return months later to complete an episode. All kitchen scenes would be done together, then all scenes in the upstairs hallway would be filmed together, etc. This fact was well concealed until Dawn Lyn joined the cast as Dodie. Her upper front teeth grew in irregularly during the entire 1969-70 season, from being barely visible in scenes with MacMurray to being plainly visible in scenes without him. William Frawley never felt comfortable with this method of filming, having grown accustomed to filming I Love Lucy in sequence during its entire run.

William Frawley really enjoyed working on the show and did not want to leave. To make matters worse, he was replaced by William Demarest, whom he hated in real life.

Don Grady almost left the show when Tina Cole was cast as Katie. In an interview, Cole revealed that Grady felt she wasn't his type. As it turned out, they eventually fell in love in real life and almost got married not once, but twice.

The show moved to CBS after ABC refused to finance the higher cost of filming in color.

Tim Considine and Meredith MacRae dated in real life while they were on the show while Don Grady and Tina Cole almost got married in real life. They broke up shortly before Grady left the show.

The show was originally going to be named The Fred MacMurray Show, but Fred MacMurray didn't like the idea.

When Don Grady left the show in the final season, his absence was explained by having Robbie get transferred to Peru by his job and have Katie join him there.

Not only was the first episode of the 1965-1966 season the series' CBS debut, it also was the first episode to be shot in color. Before taking the role of Katie, Tina Cole appeared on a couple of earlier episodes in various roles, always being cast as one of Robbie's girlfriends.

The exterior set used for the outside of the main house in the film was actually the barn from Melody Ranch (1940) with added features.

When William Frawley left the show midway through the 1964-65 season due to declining health, his absence was explained by having Bub move to Ireland to live. He was referred to several times in subsequent episodes that season, then was never mentioned again once the show moved to CBS.

Although officially leaving after the show's fifth season in 1964-1965, Tim Considine's last appearance as Mike, the eldest son, was actually in the first episode of season 6 (the series' first in color). The episode opened with a brief scene showing Mike and Sally's (Meredith MacRae) wedding. The episode also "launched" Barry Livingston ("Ernie") as the new son. The characters of Mike and Sally were mentioned in the next two episodes, which dealt with Ernie's adoption, and in a subsequent episode when Charley and the boys thought Steve was getting married. Mike was referred to by name one last time in the second 1966-1967 episode, when the gang visited Steve's hometown. After this they were never referred to by name again for the remainder of the series, although Mike was indirectly referred to as, "the first of you" by Steve a few years later.

The character 'Steve Douglas' was ranked #7 in TV Guide's list of the "50 Greatest TV Dads of All Time" (20 June 2004 issue).

With 369 episodes over 12 years, this is the second longest-running (live action) comedy in US TV history (as of February 2003), surpassed only by The Adventures of Ozzie and Harriet (1952).

The name of the town where the Douglasses lived before moving to California was Bryant Park. However, the state the town was in was never named.

June Haver, Fred MacMurray's real-life wife, recommended Beverly Garland for the role of Barbara.

Fred MacMurray renewed his contract annually during the show's entire run.

In the first years 1960 - 1964 Chevrolet was the sponsor and different models were shown throughout each show. Steve Douglas had a 1961 Impala station wagon for the first year. The ending credits also showed Chevrolet photographs which were used in the print ads of the time. In 1964 - 1970 Pontiac was the most noted car sponsor, where Steve had various blue Pontiac Bonneville station wagons while Robbie drove a 1954 Pontiac Star Chief convertible, occasionally nicknamed the "old coffee grinder" by his classmates. In 1970 - 1972, Ford Lincoln Mercury was the sponsor, and Steve had a Mercury Marquis station wagon.

According to one account, Chip was born Richard but as a toddler pronounced his name Chipper. The name stuck and as he got older it was shortened to Chip. If you'll notice his dad regularly called him Chipper.

When Barry Livingston first joined the show as Ernie, he replaced the character of Sudsy Pfeiffer as Chip's best friend. At that time, despite their noticeable age difference, both boys were in the same grade. However, once the character of Ernie was added as a regular to the series, he reverted to his actual age, three years younger than Chip, effectively establishing him as Chip's kid brother.

The character Steve Douglas is an Aeronautical Engineer specializing in Structural Design. He is also a former Test Pilot.

In its time, one of the few television shows to survive a change in networks. At the beginning of the 1965-1966 season, the show moved from ABC to CBS, where it ran for its final seven seasons.

Charley was Bub's brother.

Chip is the only son to stay for the entire series. However, he's absent during a lot of season 12, only appearing in 8 episodes. Other earlier episodes he's missing from are The Love God and The Recital.

Several years later it was revealed that there were different plans in the works for the character of Robbie when Don Grady left the show. One plan was for Robbie and Katie to divorce and another plan was to have Robbie killed off.

One of the original choices for the role of Steve Douglas was Eddie Albert.

Uncle Charley served in the Merchant Marines before coming to live with Steve and the boys.

When the character of Ernie was officially adopted by the Douglas family, his dog, Wilson, disappeared without explanation.

None of the cast members who joined the show in the color era have lasted 100 episodes or more.

This show was in the same television "universe" as Family Affair (1966) and To Rome with Love (1969) due to the fact that all three shows were produced by the same company. In fact, Robbie and Katie made a crossover appearance on To Rome with Love. Interestingly, there were no crossovers between My Three Sons and Family Affair.

The opening theme song, written by Frank De Vol, is basically a jazzed up version of "Chopsticks".

The shaggy dog on the show was trained by Frank Inn. The dog's name was Tramp.

The theme song is reminiscent of a family band. The rhythm part is Chopsticks, as would be played by a kid, with the other backing instruments being played at increasingly higher skill levels by age. The lead melody on saxophone, which is played very well, would represent the father, played by Fred MacMurray. During the sixth season, McMurray starred in the popular Boy Scout film Follow Me, Boys! (1966), in which he was a saxophone player who ends up in a small town, becomes a Scoutmaster, and becomes a guiding light for boys.

As of 2018, Barry Livingstone is the only surviving regular cast member active in in the Screen Actors Guild.

One reason William Frawley left the show was his health. Another was that the studio could no longer get insurance on him. Frawley passed away, at age 79, about a year after leaving.

The first seven seasons were filmed at Desilu Studios. The sale of Desilu to Paramount prompted filming of the series being shifted to CBS Studio City. The move largely necessitated the relocation of the family to California.

Even though Don Grady left the series after Season 11, his name remained in the opening credits in the 12th and final season.

The house on the first few seasons was in fictional "Bryant Park". This house is a real residence located at 838 5th Avenue in Los Angeles, California.

Ronne Troup, who played Chip's wife Polly, was supposed to be 18 when she was introduced. In actuality she was 25 when she first appeared on the show.

Fred MacMurray was the only cast member to appear in all three hundred eighty episodes of the series (or in other words he was always 'edited-in' after the episode was completed). Stanley Livingston did stay for the whole 12-season run, but was absent for three episodes.