When the gang finds out that Barney and Robin are hesitant to define their relationship, Lily forces them to confront their biggest fear...becoming boyfriend-girlfriend. Meanwhile, Ted is anxious about teaching his first lecture at Columbia

Barney takes Marshall, and Robin to a strip club where they find a stripper who looks almost exactly like Lily. Meanwhile, Ted discovers he had been fixed up with the same woman, Jen seven years earlier.

When Robin fears that Barney is cheating on her, she soon discovers that he is spending his evenings with Ted learning everything there is to know on how to date her.

Marshall and Lily want to hook up with Barney and Robin for double-dating and fun, but their desperate eagerness to please is a huge turn-off. Meanwhile, when a succession of girls come to his apartment and immediately fall asleep, Ted is bummed to learn he is a Sexless Innkeeper whose dates are only interested in a comfy place to crash

Barney tries his best hoping to convince Robin into becoming an American citizen, while Ted and Marshall's road trip takes an unexpected turn for the worst when Marshall invites Lily to come along.

Barney offers relationship advice that leads to Marshall and Lily having a big fight..

After Barney (Neil Patrick Harris) and Robin hit a rough patch in their relationship, Lily devises the perfect plan to break them up, calling in help from Robin’s famous friend, Alan Thicke.

Barney dusts off his "playbook" to help him back into the dating scene following his breakup with Robin....

Barney’s unhappy after a slap bet is bequeathed to Ted and Robin by Marshall. Lily’s long-absent father arrives for Thanksgiving...

When a perfect girl finally shows up, the gang tries everything to help Ted, while Marshall takes action when he discovers a letter written by younger himself.

When Marshall picks up smoking again, it prompts Lily, Ted and Barney, ex-smokers all, to succumb as well. Meanwhile, Robin gets a new co-anchor at her show...

On the 100th episode, Barney must choose if he should give up wearing suits in order to land a hot bartender, but his conflicted feelings result in an amazingly awesome musical number. Meanwhile, Ted gets closer to meeting the future mother of his kids. '

When Marshall's co-worker kisses him, he can't get Lily to believe it happened. Robin discovers she's the subject of a drinking game

When Barney is about to complete the perfect week - landing seven different girls in seven days - the gang roots him on in order to forget about their own miserable week.

After forgetting to get Ted a blind date on Valentine's Day, Lily and Marshall go after the many discarded girls Barney has dated in order to see if any of them can be Ted's future wife. Meanwhile, Robin is invited to a party by an obnoxious colleague.

When the gang tries to convince Ted that he is being strung along by Tiffany, they reflect about relationships where each of them has been in the same situation.

When Robin confesses that she is still angry with Barney for the way he handled their break-up, she enlists the help of Anita, a self-help author who plans to beat Barney at his own game.

When Ted ruins Lily's birthday dinner celebration by bringing a date, Lily goes to great lengths to keep her out of the traditional photo she takes every year of the gang.

When Marshall gets mugged, Lily decides she wants to get a gun for protection, so Marshall comes up with a convoluted story about the mugging to deter Lily from following through

When Ted attends his mother's wedding, he is extremely disturbed by her overly affectionate relationship with her fiance, which forces him to think about his own life and make an impulsive decision

When Ted and Barney jeopardize Robin's new relationship by professing their love for her, Robin realizes that she is finally over them. Meanwhile, after spending a weekend sleeping in twin beds, Marshall and Lily decide to get twin beds at home

Crashing a snobby high-society party allows Ted to show off how pretentiously intellectual he can be.

Ted discovers the date movie he sees with a girl is based on his relationship with Stella.

Marshall and Lily make a secret pact to start trying to have a baby if they ever finally see Barney's doppelganger. Meanwhile, Robin finally gets an offer for her dream job.