- “Blaine, I’m a man who’s always lived in the shadows. And everyone who’s come into my life has always tried to pull me out into the sun or push me back into the darknes,And then you came along. And even if someone had told me that it wasn’t gonna work out and that at the end of all of our struggling and all of our work, it would just end in heart ache ; I'm a working progress”
- —Kurt at Blaine during their wedding day
The first meeting of Kurt and Blaine, takes place in the episode Never Been Kissed, when Kurt is "forced" by Puck, to spy on the rival choir: the Dalton Academy Warblers, after the meeting they had with the boys, to talk about the challenge: Boys vs Girls. Kurt gets caught by Blaine and two fellow Warblers, Wes and David, where Kurt thinks it is nice of them to buy him coffee before beating him up. Blaine and Kurt have instant chemistry and soon develop a friendship. Blaine gives Kurt advice on how to handle Karofsky's bullying, and goes to Kurt's school to confront Karofsky about his actions, but when the bullying becomes unbearable, Kurt transfers to Dalton Academy and joins the Warblers in Special Education, resulting in him and Blaine continuing to grow closer. Blaine often acts as a mentor and source of courage for Kurt, before making the transition into a romantic interest.
In A Very Glee Christmas, Kurt reveals to Will that he is in love with Blaine, and that Blaine is actually gay. The two perform their first duet, Baby, It's Cold Outside. Then in Silly Love Songs, Kurt admits to Blaine that he has feelings for him after Blaine fails to serenade a guy he likes at "the Warblers Gap Attack." Blaine confesses that he has no idea what he is doing when it comes to romance, and the two agree to stay friends. They remain just friends until Blaine realizes he is in love with Kurt in Original Song (when Kurt sings Blackbird by The Beatles). This is the episode in which they share their first kiss, and it is assumed that they start dating very soon afterwards. In the episode New York Blaine tells Kurt that he loves him for the first time, to which Kurt replies that he loves him too.
Their relationship is taken to the next step in Season Three when Blaine transfers to McKinley and the New Directions, because he can't stand to be apart from the person he loves.
Kurt and Blaine share loving looks during some songs and rarely fight, only having three fights during the course of their relationship so far (The First Time, Dance with Somebody and The Break-Up). They have been dating for over a year, their one-year anniversary was on March 15, 2012. They also lost their virginities to each other in The First Time. Near the end of the year, Blaine and Kurt are dismayed by the idea of Kurt graduating and moving to New York while Blaine will be left behind for one more year. However, they persist on always being together.
Kurt and Blaine's relationship is tested when Blaine convinces Kurt to move to New York in The New Rachel, by singing It's Time to him. They maintain their long distance relationship successfully at first via skyping and texting, but with conflicting schedules, things start to slide quickly. In The Break-Up, Blaine surprises Kurt by showing up in New York early. During Blaine's acoustic performance of Teenage Dream, he becomes very emotional, which Kurt notices. Eventually, Kurt asks Blaine what the problem is, resulting in Blaine telling him that he was with someone else back in Lima (presumably Eli.C). Kurt leaves heartbroken and ends up giving him the silent treatment. In The Role You Were Born to Play, Blaine admits to Sam that since the break-up, he hasn't been the same and is afraid that he lost the love of his life. Kurt and Blaine make up in Thanksgiving, and then as a Christmas present, Burt brings Blaine to New York in Glee, Actually, and, while ice skating, Kurt and Blaine duet White Christmas. At the end of the season, Kurt arrives in Lima to support his dad at his appointment, having recently found out that Burt has stage 1 cancer, and visits McKinley with Mercedes and Mike to see the New Directions. Blaine flirts with Kurt, and in Wonder-ful Blaine asks permission from Burt to ask Kurt to marry him. Burt, while happy that Blaine is so in love with his son, explains to Blaine that they are too young, and that they are meant to be together so he should just relax and everything will be OK.
In Love, Love, Love, Blaine convinces Kurt to get back together with him, after finding out that the relationship between Kurt and Adam Crawford didn't work out, after which they sing Got To Get You Into My Life, a song prepared by Kurt and performed with a marching band. Blaine then asks the New Directions, The Warblers, the Haverbrook School for the Deaf and Vocal Adrenaline to aid him in his proposal to Kurt by singing Help!, which they all readily agree to. Burt drives Kurt to Dalton Academy, where Blaine and all the choirs proceed to sing All You Need Is Love, along with Rachel, Mercedes and Santana, before finishing at the very staircase on which Kurt and Blaine first met. Blaine gives a heartwarming speech about his and Kurt's love, before asking Kurt to marry him, which, through tears, Kurt agrees to. After graduation, Blaine gets accepted into NYADA and moves in with Kurt in New York.
Their relationship is once again tested by their new lifestyle and Kurt's newfound confidence that puts them in an uncomfortable position, and Blaine finally decides to move out to draw lines between them and learn how to live in the big city. After a while, when Rachel moves to LA, Blaine moves back in with Kurt and they live together in the loft. Blaine and Kurt broke up sometime before the beginning of the season. Their constant arguments made Kurt believe they were not meant to be after all and broke off the engagement. Blaine then returned to Lima after his depression got his grades to slip and eventually cut out of NYADA.
Kurt eventually realizes his mistake and rushes back to Lima in hopes of earning Blaine's forgiveness. Much to his disappointment, Blaine is already seeing someone: Karofsky. With Sue's help, they eventually realize their lingering feelings for each other. While originally helping out at Brittany and Santana's wedding, the brides and Sue convince them to hijack the wedding and get married alongside them.
Blaine eventually moves back to New York to attend NYU while Kurt goes back to NYADA. Five years later, they are now successful actors and parents, with Rachel as their surrogate.
On AO3, Klaine is the most written ship within the Glee tag; Kurt's most written, as well as Blaine's most written.
- Both have had crushes on other boys in the show before dating: Kurt has had crushes on Finn and Sam, and Blaine has had a crush on Jeremiah.
- In The Purple Piano Project, Kurt mentions watching 'The Bachelorette' with Blaine.
- By big parts of the fandom, kisses, cuddles and sex between the couple are known as "Klisses," "Kluddles" and "Klex," respectively, plus now "Kledding."
- Both are each other's first boyfriend.
- Both had moved to Dalton due to severe bullying.
- In I Kissed a Girl, Blaine mentions the couple enjoys singing Pink's song, Perfect, in the car together.
- Both love Vogue, Marion Cotillard, fashion and musicals.
- Blaine has a picture of Kurt on his nightstand, shown first in Michael.
- Both kiss a girl prior to their relationship: Kurt kisses Brittany in Laryngitis and Blaine kisses Rachel in Blame It on the Alcohol.
- The First Time is the first episode where Blaine calls Kurt his boyfriend.
- Both have pictures of each other in their lockers. In Never Been Kissed, Kurt has the word COURAGE made out of magazine letters, above is a picture of Blaine in his Dalton uniform. In Big Brother, you can see a poster from Kurt's campaign for class president in Blaine's locker.
- In Dance with Somebody, Kurt states that he and Blaine have scheduled make-out sessions.
- In Dance with Somebody, when Blaine says, "I love you so much," he is wearing the same cardigan that he wore when he first told Kurt that he loved him in New York.
- Rachel and Santana have indirectly sang a duet about how Kurt or Blaine feels while they are talking to that other man; A Boy Like That/I Have A Love for Blaine and Sebastian and So Emotional for Kurt and Chandler
- They apparently watch a lot of reality TV shows together including 'The Bachelorette', 'Being Bobby Brown', and 'Jersey Shore'. As shown in Props, they also went trick-or-treating and dressed up as Snooki and The Situation.
- In Extraordinary Merry Christmas, Blaine had saved Kurt's favorite gum wrapper so that he could make it into his promise ring to give to Kurt. Since it was deleted content and not in the actual episode, it was considered non-canon, until a scene in Dreams Come True, where Kurt shows Blaine his time-capsule locker and that he had kept that ring.
- Both of them ran for Senior Class President in their respective senior year. Kurt lost, but Blaine won.
- It has been implied that Kurt picks out some of Blaine's clothing in Big Brother, Movin' Out and again in New New York.
- Blaine has a scrapbook with pictures of Kurt as seen in The Role You Were Born to Play.
- Both have had a crush on Sam: Kurt in Duets and Blaine from Sadie Hawkins to Guilty Pleasures.
- Both have performed a song with the New Directions Girls while wearing an elaborate costume. Kurt, Bad Romance and Blaine, Diva.
- Santana stated in Girls (and Boys) on Film that Come What May is the song they want to sing at their wedding.
- They have had a duet in three of the Christmas episodes: Baby, It's Cold Outside in season 2, Let It Snow in season 3 and White Christmas in season 4.
- All three of the songs that Blaine sings in the courtyard are for Kurt.
- In I Do, they have sex in the hotel room number 206, similar to Never Been Kissed (2.06) which is the episode where they first meet.
- In Love, Love, Love, Kurt and Blaine share a kiss in the courtyard after singing Got to Get You into My Life which is the first time they kiss openly at McKinley High School.
- They get engaged on the same staircase that they met on.
- They are the second young couple to get engaged on the show after Finchel.
- They are the only couple in the show that gets back together and gets engaged in the same episode.
- They are also the only couple to get back together and get married in the same episode.
- "Klaine" was nominated for a People's Choice Award (2014) for Favorite On-screen Chemistry.
- Both have been part of the Cheerios at some point. Kurt was a Cheerio member during the first season, while Blaine was a Cheerio member during the fourth season.
- In The Back-Up Plan, they share more kisses and "I love you's" than any other couple in a single episode.
- In Season Five, they share more kisses than in all previous seasons combined.
- Their kiss in The Hurt Locker, Part Two lasts longer than any other kiss shown in the series.
- Kurt and Blaine have the same anniversary as Santana and Brittany since they married on the same day.
- Their first kiss was included in Glee's Top 5 On-screen Kisses countdown.
- They were included in Glee's Top 3 Unsinkable Ships countdown.
- They made it to the Top 4 of E! Online's TV's Top Couple Tournament in 2015, but lost to Once Upon a Time's Killian Jones and Emma Swan.
- They are the second couple (after Finchel) with the biggest amount of duets.