Trivia

Barney Stinson was named after a heroin peddler in the James Ellroy book 'LA Confidential'.

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".

Alyson Hannigan's character on Buffy the Vampire Slayer, Willow Rosenberg, once mentioned that she wrote Doogie Howser, M.D. 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.

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'!

One of the show's recurring gags is, whenever somebody says a phrase or word that resembles a military rank (eg. "Major buzz-kill") both Ted and Robin (and in some instances Barney, Marshall and Lily join in) salute and repeat whatever is said as though addressing a military officer ("Major Buzzkill").

Although their characters are all supposed to be the same age, there is actually a nine-year span in the actors' ages: when the show premiered, Neil Patrick Harris was 32, Alyson Hannigan and Josh Radnor were 31, Jason Segel was 25, and Cobie Smulders was 23.

Cobie Smulders and her character, Robin Scherbatsky, are from Vancouver.

Three of the main actors on the show have had their significant others in multiple episodes. Husband of Alyson Hannigan, Alexis Denisof, plays Sandy Rivers; Cobie Smulders boyfriend, Taran Killam, plays Blauman; and David Burtka, fiancé of Neil Patrick Harris, plays Scooter.

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.

Ted and his friends regularly got to Maclaren's Pub, which is a bar right next to 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 Season 7 one can see Conan O'Brien in the background at the gangs famous MacLaren's Pub

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 15 overall.