1) The characters of Ted, Marshall, and Lily are based on the show's creators, Carter Bays and Craig Thomas, and Thomas's college sweetheart and wife, Rebecca.
2) Unlike most multi-camera sitcoms, How I Met Your Mother shot episodes over a span of three days as opposed to just one.
3) Another difference was they actually filmed in a silent studio. The laugh track was added in later when they would screen the episode for an audience.
4) Barney's character was originally described as a "Jack Black, John Belushi type," but as soon as Neil Patrick Harris auditioned for the role, the creators got rid of the description.
5) During his audition, Neil Patrick Harris acted out Barney playing laser tag. He did crazy dives and rolls, even slamming into the creators' desk and knocking everything over.
6) Jason Segel was Bays and Thomas's first choice for the role of Marshall. They were both huge fans of Freaks and Geeks.
7) Casting director Megan Branman spotted Cobie Smulders doing a bit part on a drama series while flipping through channels. She immediately told the creators she had found their Robin.
9) Thomas's wife Rebecca said that they could only make a character based off her if Alyson Hannigan played the part.
10) Jim Parsons originally auditioned for the role of Barney.
11) Jennifer Love-Hewitt was originally supposed to play Robin, but she booked Ghost Whisperer instead.
12) Britney Spears reached out to the creators about wanting to be involved in the show.
13) Casting director Marisa Ross talked about casting Cristin Milioti as The Mother for two years before they called her in to audition.
14) The creators planned to make Victoria the mother if the show was cancelled during Seasons 1 or 2.
15) Josh Radnor helped the creators and music supervisor Andy Gowan choose music for the series.
16) In "Something Blue," the engagement that happened behind Robin and Ted was real. The extras were related to one of the writers and big fans of the show.
18) The idea for the "Slap Bet" between Marshall and Barney came from Bays, who would make slap bets with his high school friends.
19) MacLaren's Pub was named after one of the show's production assistants, Carl MacLaren.
20) It was modeled after the real NYC bar McGee's, where Bays and Thomas hung out when they worked on the Late Show With David Letterman.
21) The running joke "Have you met Ted?" was actually started by Bays and Thomas's boss at Letterman. He would say, "Have you met Carter?"
22) Cobie Smulders, Alyson Hannigan, and Neil Patrick Harris's real-life husbands all appeared on the show more than once.
24) Thomas and Bays decided to use two different actors for Ted — Josh Radnor and Bob Saget — so viewers would understand that Ted went on a transformative journey and wasn't the same person he used to be.
25) Barney and Robin's relationship wasn't planned from the beginning. The creators came up with the idea after seeing the chemistry between Neil Patrick Harris and Cobie Smulders.
26) Pamela Fryman directed 196 of the 208 episodes, including the series finale.
27) In the episode "Bad News," Jason Segel didn't know Marshall's dad was going to die until they shot the episode. When Hannigan said her line, "He didn't make it," we see Segal genuinely reacting to the news.
28) Neil Patrick Harris drank so much Red Bull both on screen and off while playing Barney Stinson that the company gave him a lifetime supply.
28) Jason Segel tried to kick his cigarette smoking habit because Alyson Hannigan hated the smell. They had a bet where he owed her $10 every time he had a cigarette. By the end of the first day, Segel owed Hannigan $200.
29) The actors who played Ted’s children, David Henrie and Lyndsy Fonseca, filmed their final scene in which we learn who Ted ends up with during Season 2. They were then sworn to secrecy.
30) Josh Radnor got to keep the Blue French Horn and Cobie Smulders got Robin Sparkles' jean jacket.
32) The Robin Sparkles music videos were some of the hardest scenes to shoot. They required an extra day of filming and Cobie Smulders would wind up dancing for about 16 hours straight.
33) All of the extras featured in the train station where we finally see The Mother for the first time were crew members.
34) Neil Patrick Harris's favorite episode of the series was the 100th episode, "Girls vs. Suits," in which the entire cast performed a musical number.
35) One of Alyson Hannigan's fondest memories from the series was the episode when Marshall surprises Lily at the airport with a marching band. She was pregnant IRL and got really emotional while filming.
36) The most-viewed episodes were the series finale and the Season 1 episode "The Pineapple Incident."
37) And finally, the last scene filmed for How I Met Your Mother was when Ted meets The Mother on the train platform for the first time.