All of Lyndsy Fonseca and David Henrie's scenes as Ted'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.
Barney 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.
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.
Most of the websites featured in the show such as www.canadiansexacts.org and www.stinsonbreastreduction.com are real websites. www.lilyandmarshallselltheirstuff.com was created for charity and items from the show were auctioned off.
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's dogs in Season 2, when she and Radnor's characters are dating.
In most "statistics" Barney Stinson 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 apears on page 83.
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 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.
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.
Each character in the series has had their own musical number except Lily. Ted had his own musical number called "Super Date" in the episode "Of Course" (2010) Barney has his own musical number called "Nothing Suits Me Like a Suit" in the episode "Girls vs. Suits" (2010) Robin had her own musical number (and many others) called "Lets Go To The Mall" in the episode "Slap Bet" (2006) and Marshall has his own musical number called "Marshall vs. the Machines" (2010) and that leaves Lily without ever having her own musical number
Ted and his friends regularly got 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.
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 "The Possimpible" 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.
Writers/producers/co-creators Carter Bays and Craig Thomas are members of the band "The Solids," which performs 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 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.
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".
When Ted meets Klaus, Victoria'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" doesn't actually exist in Germany or other German-speaking regions.
Anne Dudek, who plays the girl whom Ted breaks up with repeatedly on her birthday, also played Precious on an episode of Friends. 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.
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.
Dave Coulier (Joey on Full House) 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."
Four people in Marshall's family have names that start with Mar: Marshall's brothers Marcus and Marvin jr, Marshall's dad Marvin, and Marshall himself. This does not include Marcus' children, whose names all also start with "Mar".
The Royal Diner that can be seen in the background of some street episodes is the same as the one seen on the show "Bones". Which coincident Alyson Hannigan and David Boreanaz co-starred together on Buffy the Vampire Slayer.
Many SNL cast members have appeared on the show including Chris Elliot, Abby Elliot, Will Forte, Martin Short, Jerry Minor, Chris Kattan, Taran Killam, Casey Wilson, Paul Shaffer, and Bob Odenkirk (writer, but appeared in sketches)
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.
In S4E23 "As Fast As She Can", Barney 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.
Jennifer Morrison (Ted's girlfriend Zoey in season 6), Anne Dudek (Ted's girlfriend in season 1) and Kal Penn (Robin's ex-boyfriend Kevin in season 7) also had starting roles in another show, "House, M.D.", as Cameron, Amber and Kutner, respectivelly
In the earlier episodes of HIMYM, Robin'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." 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."
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, Barney ignores this every time and claims that he is Ted's best friend.
When Robin and Marshall 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.
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.
If you watch throughout the episodes, you can see Robin, Lily, and Stella 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?"
In one episode, Robin 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".
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".
The trivia items below may give away important plot points.
In the episode where Ted and Robin 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 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.
An on-going joke in the show is that nobody ever finds out what Barney'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 Magicians Code when Barney is arrested for trying to sneak a magic trick through security he is taken to airport prison. That actually happened to Neil Patrick Harris which is where Carter Bays and Craig Thomas got the idea for that episode.
The show's opening theme song and the photos displayed during it differ in only four episodes throughout nine seasons. "Hopeless" shows the main characters playing various instruments, "Bedtime Stories" is played to the tune of a music box, "46 Minutes" excludes Lily and Marshall after they move to the suburbs with new photos of Ted and Robin looking annoyed with Barney and "How Your Mother Met Me" shows Tracy with several of her friends. "46 Minutes" has a second version later in the episode to a Russian theme with Stripper Lily and her boyfriend.
Marshall and Lily agree that they won't try to have a baby until they find Barney's doppelganger. They don't follow their agreement and start trying; however, they could not get pregnant until, they go see Dr. Stengel, who turns out to be Barney's doppelganger. Lily becomes pregnant only after the appointment.
In Season 1, Marshall and Lily wanted to get married at the "Van Smoot House", and ended up getting married there at the end of Season 2. Later in the Season 6 episode "Natural History", Arthur Hobbs of GNB first introduced Barney and Marshall to George Van Smoot, or better known as "The Captain".
Before being picked up for another season, the writers planned for Victoria to be the mother. The show would end with the shot of her at Claudia and Stuart's wedding followed by Ted saying, 'and that's how I met your mother'.
When Lily and Marshall make lists of baby names, the first one Lily (Alyson Hannigan) suggests is Tara, which is the name of Willow's (Alyson Hannigan's character in Buffy the Vampire Slayer) girlfriend.
They said seeing the bride in her dress before the wedding was bad luck. Barney saw Robin before the wedding and they got divorced. Ted and Tracy also saw each other before the wedding, and then Tracy died.
In the episode Slap Bet, Barney chooses 5 slaps for eternity after Marshall wins the slap bet. However Marshall ends up getting 8 slaps throughout the series. One in the episode Slap Bet, the second one in the episode Stuff, the third in Slapsgiving, the fourth in Slapsgiving Two. In Disaster Averted, Marshall is awarded 3 more slaps in exchange for Barney not wearing the Ducky tie. He uses two of them leaving him with two more which he uses in Slapsgiving Three and End of the Aisle.
In the season 7 episode "good crazy", Ted 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, 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.
In the episode where Ted and Lily argue about if there should be a band or a DJ at Barney and Robin'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.
In the end of Sandcastles in the Sand Barney and Robin hook up for the first time after Robin is dumped by Simon and invites Barney to watch the music video after which they have sex. In the 5th season in the episode "The Rough Patch" Barney and Robin break up and Barney discovers that Robin had an embarrassing T.V show according to Alan Thicke. He then storms out of the bar to find it, this shows that what started from a Robin Sparkles video ended on a Robin Sparkles video.
Lily and Marshall make a deal with the "universe" saying that they wont get pregnant until they see Barney's döppelganger. When Lily imagined she saw Barney's döppelganger but it was'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 döppelganger. And they get pregnant a few episodes later on.
Marshall and Lily both saw each other before their wedding and lived happily ever after. Ted and Tracy saw each other before their wedding and she died. Barney and Robin saw each other before their wedding and got divorced.
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.
In the song "Let's go to the mall" sang 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.
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 someone named Tracy.