The first season introduces the six main characters: Rachel, Monica, Phoebe, Joey, Chandler and Ross. Rachel arrives in New York after leaving her fiance at the altar, and begins living with Monica in her apartment. Ross struggles to tell Rachel that he loves her, while his estranged lesbian wife is pregnant with his baby. Joey is shown to be a struggling actor, while Phoebe works as a masseuse. Chandler breaks up with girlfriend Janice (Maggie Wheeler), who frequently returns throughout the ensuing nine seasons. At the end of the season, Chandler accidentally reveals that Ross loves Rachel, who finds that she feels the same way. The second season begins with Rachel discovering that Ross is dating Julie (Lauren Tom), someone he knew from grad school. Rachel's attempts to tell Ross she likes him mirror his own failed attempts in the first season, although the characters eventually begin a relationship that lasts into the following season. Joey gets a part in a fictionalized version of the soap opera Days of our Lives, but is killed off after claiming he writes many of his own lines. Monica begins dating Dr. Richard Burke (Tom Selleck), who is recently divorced and 21 years older than her. In the season finale, they end their relationship when they realize that he does not want any more children and she does.

Season three takes on a significantly greater serialized format.[15] Rachel begins working at Bloomingdales and Ross becomes jealous of her coworker, Mark. Ross and Rachel temporarily break up; however, Rachel decides to make it permanent when Ross sleeps with someone else. After believing to have no family except for her twin sister Ursula, Phoebe becomes acquainted with her half-brother (Giovani Ribisi) and mother (Teri Garr). Joey develops a relationship with his acting partner Kate (Dina Meyer), and Monica begins a relationship with millionaire Pete Becker (Jon Favreau).

In the fourth season premiere, Ross and Rachel reconcile, but soon break up again. Phoebe becomes a surrogate mother for her brother and his wife (Debra Jo Rupp). Monica and Rachel are forced to switch apartments with Joey and Chandler after losing a bet, but manage to switch back by bribing them with Knicks season tickets and a one-minute kiss between themselves. Ross begins dating an English woman called Emily (Helen Baxendale), and the season finale features their wedding in London. Chandler and Monica sleep together, and Rachel decides to attend Ross and Emily's wedding. While saying his vows, Ross accidentally replaces Emily's name with Rachel's, to the shock of the guests.

Season five features Monica and Chandler trying to keep their new relationship a secret from their friends. Ross and Emily's marriage is called off, while Phoebe starts a relationship with police officer Gary (Michael Rapaport). Monica and Chandler go public with their relationship, to the surprise of their friends. They decide to get married on a trip to Las Vegas, but decide not to after witnessing Ross and Rachel drunkenly stumble out of the wedding chapel. In the sixth season premiere, Ross and Rachel's marriage is established to be a drunken mistake and they divorce. Monica and Chandler decide to move in together in her apartment, and Rachel moves in with Phoebe. Joey lands a role on a cable television series called "Mac and C.H.E.E.S.E", where he stars alongside a robot. Ross gets a job lecturing at New York University, and starts dating his college student, Elizabeth (Alexandra Holden). Phoebe and Rachel's apartment catches on fire, and Rachel is forced to move in with Joey while Phoebe moves in with Chandler and Monica. Chandler decides to propose to Monica, while she considers going to back to Richard, who confesses to her that he still loves her. Monica decides to accept Chandler's proposal, and the friends celebrate.

The seventh season mainly follows various antics by Monica and Chandler, who are preparing for their wedding. Joey's television series "Mac and C.H.E.E.S.E" is canceled, but he is offered his old job back on Days of our Lives. Phoebe's apartment is fixed, but due to the way it is built, Rachel decides to stay with Joey. The season finale stars Monica and Chandler's wedding, and Rachel is revealed to be pregnant.

The eighth season's first three episodes follow a "Who's the father?" format. The father of Rachel's baby is revealed to be Ross, and they decide to have the baby. Joey develops romantic feelings for Rachel, however she does not feel the same. Rachel gives birth to baby Emma in the season finale, and Ross decides to propose. Joey finds Ross's ring on the floor, and Rachel believes he is proposing and accepts.

Season nine begins with Ross and Rachel living together with baby Emma. Monica and Chandler decide to conceive a child of their own, but discover that both of them are physically unable to conceive. Phoebe begins dating Mike Hannigan (Paul Rudd), and chooses to be with him over her friend David (Hank Azaria). The group travels to Barbados in the finale to hear Ross give a keynote speech at a Paleontologist conference. Joey and his girlfriend Charlie (Aisha Tyler) break up, and she begins a relationship with Ross. Joey and Rachel's feelings for each other return, and the finale ends with them kissing.

The tenth season closes several long running storylines. Joey and Rachel try to contend with Ross' feelings about them being together, and decide to remain friends. Phoebe and Mike get married, while Charlie breaks up with Ross. Monica and Chandler decide to adopt a child, and meet Erica (Anna Faris), who gives birth to twins in the series finale. Monica and Chandler move to the suburbs, and Joey becomes upset with the changes happening in his life. Rachel takes a job in Paris, but decides not to go and resumes her relationship with Ross.