All of Lyndsy Fonseca and David Henrie's scenes as Ted (Josh Radnor)'s future children were filmed during the first season to keep them the same age throughout the series. This includes a scene for the show's eventual final episode that includes the titular Mother which were filmed early in the second season.
Due to Jason Segel's (Marshall) real-life smoking habit, he and his co-star and on-screen wife, Alyson Hannigan (Lily), rarely kissed on-screen during the run of the show; kisses between the two were infrequently scripted, at Hannigan's request, because she disliked the taste and smell of smoke on Segel's breath.
Barney (Neil Patrick Harris) is truly the inventor of "The Bro Code" (the rules which he feels a man must follow in order to be considered a "bro"). According to the number of Google searches, the phrase was non-existent until 2008.
Most of the websites featured in the show such as canadiansexacts.org, stinsonbreastreduction.com, extremitiesquarterly.com and balloonexplorersclub.com are real websites. lilyandmarshallselltheirstuff.com were created for charity and items from the show were auctioned off.
Because of the numerous scenes and the quick-cut nature of the show's visual style, the show is filmed without the traditional live studio audience. The finished episode is later shown to an audience, and their reactions are recorded and added for broadcast. The series' creators joke that the long set-up time between scenes would cross the line from "studio audience" to "hostage situation."
In an episode where Barney (Neil Patrick Harris) is challenged to pick up a girl in a bar by calling an ambulance, Carter Bays and Craig Thomas, the creators of the show can be seen as the actors playing the paramedics.
Ted (Josh Radnor) and his friends regularly go to MacLaren's Pub, which is a bar right below Ted's apartment. The pub was named after Carl MacLaren, who is the associate producer, assistant to Carter Bays. Also, a bartender named Carl plays a minor role in the show.
In most "statistics" Barney Stinson (Neil Patrick Harris) expresses, the numbers 83 or 8 and 3 are involved. And in one instance, when he posed as an elderly man, he claimed his age was 83. In another, Barney wants to get in bed with a woman from a magazine, and her picture appears on page 83.
Although singers Britney Spears and Katy Perry were two of the biggest guest stars, fashion designer Tim Gunn was the most welcomed guest star from the cast and crew. Nearly everyone on set wanted an autograph from him.
In season 4 when referring to the child he hired to act as his son, Barney makes a comment how child actors were better in the 80's. Neil Patrick Harris who plays Barney was himself a child actor in the 80s.
Alyson Hannigan was pregnant while filming many season four episodes, but the show-runners were not interested in her character, Lily, also being shown as pregnant. Most episodes used time-honored TV tricks to hide Hannigan's pregnancy, including baggy tops and giant handbags, but the episode How I Met Your Mother: The Possimpible (2009) showed Hannigan's pregnancy bump in the context of a subplot in which Lily wins a hot dog-eating contest and has a comically distended stomach afterward. A similar visual gag was used in the sitcom Titus (2000) several years earlier. Actress Cynthia Watros was pregnant during the show's second season, although her character "Erin" was not meant to be pregnant. So, in addition to the "time-honored TV tricks" being used to hide Watros' pregnancy, a flashback scenario was used in one episode that showed her character Erin winning a pie-eating contest and her actual pregnant belly was shown afterwards. After Hannigan told the show-runners that she was pregnant, Cobie Smulders discovered that she was also pregnant. Neither of the characters they play were pregnant on the show, so the costumers had the job of simultaneously hiding the pregnancies of the series' two main female actors.
Alicia Silverstone was originally cast as Stella Zinman but dropped out of the role. Reports at the time indicated that upon learning that Britney Spears would be playing her receptionist Abby, Silverstone's reps had her withdraw from the role because they did not want her first appearance on the series to be overshadowed by Spears.
Writers/producers/co-creators Carter Bays and Craig Thomas are members of the band "The Solids," who perform the show's theme song "Hey Beautiful". The Solids' first performance was at Wesleyan University, which is the alma mater of both Bays and Thomas, as well as of the characters Ted, Marshall, and Lily.
If one were to discount Robin (Cobie Smulders), since she is a main character, then the ex-girlfriend of Ted's (Josh Radnor) who has appeared in the most episodes would be Victoria (Ashley Williams), with 16 overall.
When Ted (Josh Radnor) meets Klaus (Thomas Lennon), Victoria (Ashley Williams)'s German fiancé, they speak a few words in German. One term Klaus uses is "Lebenslanger Schicksalsschatz", which translates into "lifelong treasure of destiny". While the words "lebenslang" (lifelong), "Schicksal" (destiny) and "Schatz" (treasure) are real German words, the term "Lebenslanger Schicksalsschatz" was simply made up for the show and doesn't actually exist in Germany or other German-speaking regions.
Anne Dudek, who plays the girl whom Ted (Josh Radnor) breaks up with repeatedly on her birthday, also played Precious on an episode of Friends (1994). Precious is the ex-girlfriend of Mike (Paul Rudd) who he has to break up with upon returning from Barbados in Season 10, Episode 1. The day of the break-up turns out to be her birthday.
When both Samm Levine and Neil Patrick Harris were on Kevin Pollak's Chat Show (2009), Levine said that he was called to audition "more than once" for the role of Barney Stinson, even though he himself thought that he was wrong for the role. Levine told Harris that he thought Harris was better as Barney than he would have been.
Before co-starring in the show, Josh Radnor and Neil Patrick Harris appeared in a stage production of John Robin Baitz' play "The Paris Letter" in 2004, in which they played lovers, each walking onto the stage fully nude.
When Neil Patrick Harris directed a 2010 limited-run production of the musical "Rent" at the Hollywood Bowl, he cast Wayne Brady in the role of Tom Collins, after Brady and Harris had previously played brothers on "How I Met Your Mother".
Dave Coulier (Joey on Full House (1987)) made a cameo in an episode on Season 8 where he recites his famous "Cut It Out" line to which Bob Saget (Future Ted Narrator & Co-star alongside Coulier as Danny on Full House) narrators that part as "I always liked that joke."
In the episode "Blitzgiving", the Blitz (Jorge Garcia) gives some 'random' numbers to form a phone number to send a picture of Marshall (Jason Segel)'s junk. He gives the lottery numbers his character Hurley from Lost (2004) had when he won the lottery: 4 8 15 16 23 42.
In Season 6, Marshall (Jason Segel) and Robin have never hung out alone. However, in an earlier season, Marshall and Robin (Cobie Smulders) went to a Minnesota and Canadian bar together several nights in a row.
Four people in Marshall's family have names that start with Mar: Marshall (Jason Segel)'s brothers Marcus (Ned Rolsma) and Marvin jr (Robert Michael Ryan), Marshall's dad Marvin (Bill Fagerbakke), and Marshall himself. This does not include Marcus' children, whose names all also start with "Mar".
Jason Segel was cast for the role of Marshall Eriksen because of his work on the short lived television show Freaks and Geeks (1999), of which HIMYM creators Carter Bays and Craig Thomas were huge fans. Besides Segel, other three actors from the "Freaks and Geeks" cast appeared on the show. Samm Levine played Phil on season 1 episode 5, "Okay Awesome", Martin Starr played Kevin on season 1 episode 8, "The Duel", and Busy Philipps played Rachel on season 3 episode 3, "Third Wheel".
In the earlier episodes of HIMYM, Robin (Cobie Smulders)'s father was played by Eric Braeden, who has also played the part of Victor Newman for literally decades on the daytime drama, The Young and the Restless (1973). Then, in the later episodes of HIMYM, Robin's father was played by Ray Wise, who has for many years played the part of Ian Ward, one of Victor Newman's main antagonists on "The Young and the Restless."
In S4E23 "As Fast As She Can", Barney (Neil Patrick Harris) is trying to talk his way out of a traffic ticket. In S2E17 "Arrivederci, Fiero" it is revealed that Barney has a fear of driving. Thus giving the impression that he has learned how to drive, and his issues with buying a car in New York.
In one episode, Robin (Cobie Smulders) deletes a contact from her phone, the camera captures the next name in her phone, "Dan Blocker". Dan Blocker is the deceased actor that played " Hoss Cartwright" on the TV series Bonanza (1959).
Alyson Hannigan's character on Buffy the Vampire Slayer (1997), Willow Rosenberg, once mentioned that she wrote Doogie Howser, M.D. (1989) fan-fiction as a girl. Hannigan went on to star in "How I Met Your Mother" with Neil Patrick Harris, who as a boy played Doogie Howser. Alyson Hannigan' who plays Lily, is perhaps best known prior to starring in 'How I Met Your Mother' for her role on "Buffy the Vampire Slayer". The creators of both of these shows - Joss Whedon of the Buffy series and Carter Bays and Craig Thomas of HIMYM - all graduated from Wesleyan University, as well as did the characters Lily, Ted, and Marshall on HIMYM. Additionally, Hannigan's character from the Buffy series, Willow, got early acceptance to Wesleyan, along with many other schools. Several cast members have also worked with Joss Whedon, notably stars Alyson Hannigan' (Buffy the Vampire Slayer), Neil Patrick Harris (Dr. Horrible's Sing-Along Blog) and Cobie Smulders (The Avengers). Also appearing have been guest stars Morena Baccarin (Firefly/Serenity), Alexis Denisof (Buffy the Vampire Slayer/Angel/Dollhouse), Amy Acker (Angel/Dollhouse), Tom Lenk (Buffy the Vampire Slayer/Angel), Harry Groener (Buffy the Vampire Slayer), Danny Strong (Buffy the Vampire Slayer). The search for all the main characters' so-called "doppelgangers" is a running joke throughout this series. In 'Buffy the Vampire Slayer' doppelgangers were also a frequent theme of many episodes, and most of the major characters (including Buffy, Xander, and Willow) encountered doubles of themselves through plot contrivances of magic or alternate universes.
On the Still Buffering podcast, HIMYM guest star Lin-Manuel Miranda mentioned that Rebecca Alson-Milkman (co-creator Craig Thomass wife and the inspiration for Lily Aldrin (Alyson Hannigan)) was a friend of his in high school theatre in NYC. They stayed pen pals when she went off to Wesleyan, then Miranda attended the same college where he reconnected and watched her and Thomas's romance begin.
In season 8 episodes 11 & 12 the new GNB building opens up, however they never seem to move into the building. All episodes after that with scenes at GNB still show Barney (Neil Patrick Harris) in his same office.
One ongoing joke is that a favorite topic is "Who is Ted's 'best friend'". Even though it is already confirmed that it is Marshall (Jason Segel), Barney (Neil Patrick Harris) ignores this every time and claims that he is Ted (Josh Radnor)'s best friend.
Is season 6 episode 4 (Subway Wars) Ted (Josh Radnor) points out the Arcadian Hotel to the bus driver. The next episode (Architect of Destruction) is where he finds out that is the spot of the new GNB headquarters and it will be torn down.
When Robin (Cobie Smulders) and Marshall (Jason Segel) go into the Little Minnesota bar, a woman is seen wearing a Minneosta Vikings jersey that has the last name Smulders on it. This also refers to Cobie Smulders who plays the character of Robin.
If you watch throughout the episodes, you can see Robin (Cobie Smulders), Lily (Alyson Hannigan), and Stella (Sarah Chalke) wearing the same necklaces on different characters. Also, at the end of S3 E20 "Miracles", the woman at the bar has the EXACT same purse as the woman in the opening scene of S4E1 "Do I Know You?"
The trivia items below may give away important plot points.
In the episode where Ted (Josh Radnor) and Robin (Cobie Smulders) break up, there was a real life proposal During the episode, a ring was in a champagne glass and Robin thought Ted was proposing. However, the ring belonged to a man at the next table. He planned his proposal with the producers and now that couple's engagement will live forever on the show.
The mother's first name is already mentioned in season 1 episode 9, when a stripper tells Ted (Josh Radnor) she's called Tracy and Ted's off-voice tells his children 'this is the true story of how I met your mother'. The kids' shocked reaction reveals that it's the real name of their mother.
In the DVD commentary for the Pilot episode, Josh Radnor reveals that he is allergic to dogs, something the creators didn't know until Radnor was cast. That may have played a part in the decision to get rid of Robin (Cobie Smulders)'s dogs in Season 2, when she and Radnor's characters are dating.
An on-going joke in the show is that nobody ever finds out what Barney (Neil Patrick Harris)'s job is. Every time the gang ask him he sarcastically replies, 'Please'! In the final season, it is revealed that PLEASE actually stands for Provide Legal Exculpation And Sign Everything.
In the Episode How I Met Your Mother: Bad News (2011) (S6E13), there is a countdown of hidden numbers that starts with "50" at the beginning of the episode and ends with "1". This is seemingly counting down to Marshall (Jason Segel)'s father's death which is announced right after the countdown is finished.
Before being picked up for another season, the writers planned for Victoria (Ashley Williams) to be the mother. The show would end with the shot of her at Claudia (Virginia Williams) and Stuart (Matt Boren)'s wedding followed by Ted (Josh Radnor) saying, 'and that's how I met your mother'.
In the season 7 episode How I Met Your Mother: Good Crazy (2012), Ted (Josh Radnor) starts up online dating and finds a girl that seems to be perfect for him. However, after emailing her, it's revealed to be Barney (Neil Patrick Harris), simply testing Ted. If you pause it and read "the girl's" description, you'll see Barney actually address Ted at the very end of the description.
As it started to gain momentum, "How I Met Your Mother" was often criticized for copying Friends (1994). In the Season 2 "Crazy Eyes" episode, the HIMYM writers shot back with, "Well, it's official - hanging out in a coffee shop is way less fun than hanging out in a bar."
Marshall (Jason Segel) and Lily (Alyson Hannigan) agree that they won't try to have a baby until they find Barney (Neil Patrick Harris)'s doppelganger. They don't follow their agreement and start trying; however, they could not get pregnant until, they go see Dr. Stangel, who turns out to be Barney's doppelganger. Lily becomes pregnant only after the appointment.
In the episode where Ted (Josh Radnor) and Lily (Alyson Hannigan) argue about if there should be a band or a DJ at Barney (Neil Patrick Harris) and Robin (Cobie Smulders)'s wedding, Ted votes for a DJ. However, at the very first episode, before Ted meets Robin and talks to Carl's Lebanese girlfriend, he points out that, in his opinion, a band is better. This can be explained by Ted secretly opposing their marriage.
Lily (Alyson Hannigan) and Marshall (Jason Segel) make a deal with the "universe" saying that they won't get pregnant until they see Barney's doppelgänger. When Lily imagined she saw Barney (Neil Patrick Harris)'s doppelgänger but it wasn't, Marshall just went along with it and they tried to have a baby but did not succeed. When they go to see a doctor to find out why they weren't getting pregnant, the doctor was Barney's doppelgänger, and they get pregnant a few episodes later on.
In an early episode Marshall (Jason Segel) threatens to beat up a guy that is cleaning a stain on Lily (Alyson Hannigan)'s butt, though he claims he's never been in a fight before. Then in a later episode Marshall says he used to get in fights with his brothers all the time when he beats up Doug.
In the song "Let's Go to the Mall", sung by Robin, there is a line says that she meets a boy in the food court that has a hair style like Wayne Gretzky. In the last season at Barney and Robin's wedding , Barney gets her an autographed photo of Gretzky as a surprise.
A possible future occupation for Marshall is implied by his name, since he was elected to the New York Supreme Court. (Actually, the highest court in New York is known as the New York Court of Appeals). Three justices of the Supreme Court of the United States had the name "Marshall". Justice John Marshall was Chief Justice of the Supreme Court from 1801-1835, Associate Justice John Marshall Harlan was on the court from 1877-1911, and Associate Justice Thurgood Marshall served from 1967-1991. Also, all three of these justices were on the Court for 34 years, the first two ending with their respective deaths and the third with his retirement. Whenever Justice Marshall Erickson is named to the SCOTUS, it may be understand his tenure as being 34 years long.
When Ted's parents come to visit, and tell Ted they are divorced, Ted asks how they met. Then they said at an Irish bar. Which is where Robin and Ted met, MacLarens Pub. Also that Ted is like his father, and Robin like Ted's mother, because neither of them wanted kids. So the show is implying that Robin is the kids mother, but on the last episode , it is confirmed that their mother is named Tracy.