Ross decides to get back together with Rachel and breaks up with Bonnie. However, Rachel wants him to take full responsibility for "cheating" on her, whereas Ross insists that they were on a break. Unable to agree on whether or not Ross cheated, they break up again. Throughout most of the season the pair frequently bicker, and snipe at one another. After Phoebe learns the older Phoebe is her real mother, she tells her twin sister, Ursula, who knew all along because she had their "mother's" suicide note, which she had not shared with Phoebe. Phoebe agrees to be a surrogate mother for her half-brother Frank and his wife Alice (who was his home economics teacher). Luckily, after having fertility treatment she becomes pregnant. Though to everybody's surprise, she is pregnant with triplets.

Joey begins dating an actress, Kathy, but Chandler likes her as well. Joey and Kathy break up after Kathy kisses Chandler. Joey is angry, but forgives Chandler when he sees that Chandler and Kathy genuinely love each other. Chandler suspects that Kathy is sleeping with a fellow cast member after watching one of her plays. He then proceeds to confront and accuse her. She is insulted and later does sleep with the cast member, so she and Chandler break up.

Monica and Rachel have to switch apartments with Joey and Chandler after losing a bet. The girls hate their new apartment, and try to convince Joey and Chandler to switch apartments in exchange for season passes to the Knicks. Instead, they agree to an all or nothing bet. The guys win, but while they're at the game, the girls switch the apartments back. They negotiate with the angry Joey and Chandler by offering them an opportunity to watch Monica and Rachel kiss for one minute, thus winning back their apartment.

Rachel's British boss asks her to take his niece Emily to the theatre; however, Ross ends up taking her, as Rachel is more interested in getting a date with a good looking customer. Ross and Emily hit it off and they quickly get engaged. The group travels to London for the wedding, except Phoebe, who is in her last trimester of pregnancy, and Rachel, who doesn't want to see Ross get married. At the wedding rehearsal dinner, Monica becomes depressed because she is mistaken as Ross' mom, and bothered by the fact that she isn't married. Chandler comforts her, and they unexpectedly end up sleeping together. Rachel realizes that she still loves Ross and goes to London to tell him. When she gets there, she sees him with Emily and decides it would not be right to ruin the wedding. The wedding goes ahead, but comes to an abrupt halt when Ross says "I, Ross, take thee, Rachel" instead of Emily. The season ends with the preacher asking whether to continue the ceremony.