After sharing a kiss at the beginning of the summer, Robin and Barney are unsure how to handle their mutual attraction. After some consideration they tell the gang they have decided to remain just friends, but secretly continue seeing each other. They are able to get away with their secret romance for a couple months, but are discovered when Ted, Marshall and Lily walk in on them together. They explain to the gang that they are happy with their casual relationship, and didn’t want to complicate it by defining it. This is unacceptable to Lily, who pressures them to label their situation, and ultimately locks them in Robin’s room to force them to address it. Meanwhile, Ted is anxious about his first days as a professor at Columbia, which is made worse when he shows up at the wrong class and starts his lecture.

Ted is trying to keep his architecture firm afloat by doing an all-nighter, but Marshall tries to lure him to the roof for a surprise 31st birthday party, on the fourth season finale.

Ted is trying to find a new job, and when an old acquaintance tries to help nothing goes as planned. Barney tries to smooth talk his way out of a ticket.

Ted ponders how being in the right place at the right time can impact a person’s life; Barney celebrates his 200th female conquest.

Ted breaks one of Barney and Marshall’s relationship rules, texting a woman he recently met, so the pair play a joke on Ted by pretending to be the woman.

Ted goes out on his own as an architect and hires an intern to help get things started, but the intern gets a little too close to others in the gang.

When Barney learns Ted has a list of things he thinks the gang is too old to do, he sets out to do every task within 24 hours in order to prove Ted wrong.

Marshall and Barney lie to keep Ted from finding out the headquarters he’d been hired to design for GNB has been cancelled.

Ted learns that not only did Lily plant another woman’s earring in his bed for Karen to find, she has meddled in some of his other relationships as well.

Marshall and Lily are less than thrilled when they hear that Ted’s college girlfriend (Laura Prepon) has moved to New York.

The gang thinks that Barney must have a secret girlfriend after noticing his bizarre behavior.

Robin, desperate to find a job before she is deported, agrees to let Barney produce a video resume for her.

Lily and Marshall try to continue their airport reunion tradition. Barney and Ted offer to keep MacLaren’s open during a blizzard so they can meet up with some college girls.

Ted and Robin discover that sex with each other solve their fights as roommates, which makes Barney very jealous and angry. Meanwhile, Marshall reveals that he’s too embarrassed to use the office bathroom.

Ted tries to keep his irresponsible sister from hooking up with Barney during her trip to New York, and Robin starts hanging out with Marshall at a bar for Minnesotans, not telling them that she’s really Canadian.

Ted (to prove he’s not a milquetoast) and Barney (to impress Robin) pick a fight with a group of guys sitting in the gang’s favorite booth at MacLaren’s.

The gang learns a new way to get their dates to sleep with them after Ted walks in on Robin’s date sitting naked on the couch.

A birthday party for one of Lily’s co-workers leads to Robin connecting with a group of single partiers known as the “Woo Girls”. Ted presents a plan for Goliath National Bank’s new HQ.

Barney creates a holiday to celebrate not being a father. Meanwhile, Lily and Marshall are considering having a baby, but Lily first wants advice from Ted and Robin.

A serendipitous meeting with someone from his past has Ted thinking about how he would handle running into someone he would prefer to forget.

Ted and Stella move up their wedding date, but the wedding may not go off as planned after Ted breaks the “No Exes Rule” and invites Robin to come in from Japan for the wedding.

When Ted is packing his stuff for his move to New Jersey, he discovers that the gang was going to hold an intervention for his engagement to Stella and demands they hold it anyway.

When Stella’s babysitter cancels, a night out turns into the gang hanging out at her place, and Ted talks up New Jersey… until he learns Stella wants him to move there after marriage.

Marshall claims that he had the best hamburger in the world during his first week in New York City, but he forgot where the burger joint is located. The gang then hits the streets of Manhattan to help him find it.

Ted and Stella get engaged, but Ted soon learns that he doesn’t know anything about her. Meanwhile, Barney confesses to Lily that he’s in love with Robin.

Ted is in a car accident that prompts Marshall to talk about miracles. Everyone flashbacks to prior moments in their lives.

When Barney and Abby realize that they have one thing in common – their mutual hatred of Ted – the “couple” decides to go to the bar to flaunt their new relationship in Ted’s face.

Barney gets a new wingman and Ted meets Stella’s daughter.

Barney and Marshall have a discussion about “The Bro Code” because Barney has broken it and wants advice.

Robin’s musical past emerges again as the group learns of someone named Simon from Robin’s past. Barney searches for more Robin Sparkles memorabilia.

After Marshall witnesses a work buddy get yelled at after handing in a report, he becomes paranoid that the same will happen to him.

Barney’s efforts to hook up with women are being thwarted by a mysterious woman from his past. Barney and the gang must sift though his many past flings in an attempt to find out who she is.

Ted pursues a woman named Stella, but only gets attention from her receptionist Abby.

Ted lives like there’s no tomorrow during a St. Patrick’s Day celebration with Barney. Lily and Marshall spend the evening at their new apartment with Robin.

Ted’s upcoming date with his doctor leads the gang to give him their own examples of why dating someone you already see regularly is a bad idea.

When Barney loses his way with women, he hopes a trip to the Victoria’s Secret Fall Fashion Show will help him regain his form.

Lily and Marshall have their first Thanksgiving as a married couple; Barney is tortured by the slap bet countdown clock, worrying about when the slap will be dished out.

Marshall awaits his bar exam results; Ted introduces his latest girlfriend to the gang, who all see the flaw that Ted has missed

Marshall and Lily’s plan to buy an apartment is hampered by mistakes and Lily’s hidden debt.

Marshall has to contemplate giving up his plan of using his law degree to help the planet when he’s courted by a major firm; Lily reveals a secret to Robin that not even Marshall knows; Ted discovers a porn actor is using his name