The first season introduces the six main characters and establishes that Ross has been infatuated with Rachel since the characters attended high school. Several episodes revolve around his attempts to tell her how he feels. She eventually finds out in the season finale. Meanwhile, Ross' ex-wife Carol is pregnant with his baby. This puts him and Carol's partner Susan in an awkward position. When the baby is born at the end of the season, Ross, Carol, and Susan agree to name him Ben. The episodic nature of the season sees the other characters having multiple dates, many of which go wrong (Monica dates a minor in one episode, for example). The recurring character of Janice (played by Maggie Wheeler) is introduced as a girlfriend Chandler breaks up with in an early episode but frequently returns to through the ensuing ten seasons.
The second season features more serialized storylines; it begins when Rachel discovers that Ross is dating Julie (played by Lauren Tom), someone he knew from grad school. Julie returns for several episodes early in the season. Rachel's attempts to tell Ross she likes him mirror his own failed attempts in the first season, though the characters eventually begin a relationship that lasts into the following season. Joey, a struggling actor in the first season, gets a part in a fictionalized version of the soap opera Days of Our Lives but loses the part soon after when he angers the writers by saying in an interview that he writes many of his own lines. Tom Selleck begins a recurring guest role as Dr. Richard Burke. Richard, a friend of Monica and Ross' parents who is recently divorced and with grown children, is 21 years older than Monica; in the season finale, they end the relationship when they realize that he does not want any more children and she does. The second season also served to deepen Chandler and Joey's friendship. This becomes especially apparent in the episodes in which Joey temporarily moves out and a creepy guy named Eddie moves in.
Season three took on a significantly greater serialized format. Rachel begins working at Bloomingdales and Ross becomes jealous of her coworker, Mark. Ross and Rachel break up after Ross sleeps with the hot girl from the copy shop, Chloe. His insistence that he and Rachel were "on a break" becomes a running gag through the remaining seasons. The two show significant animosity towards each other through the second half of the season, though the cliffhanger ending suggests the two reconcile. Interestingly, the first episode after they break up doesn't focus on the two of them, but on Chandler, who's having a very hard time dealing with the situation, as it reminds him of his parents' divorce. Phoebe, established as having no family except for an identical twin sister, becomes acquainted with her half-brother (played by Giovanni Ribisi) and in the finale discovers her birth mother she never knew she had (played by Teri Garr).
During the fourth season, actress Lisa Kudrow became pregnant. This was written into the show by having Phoebe become a surrogate mother to the children of her brother and his wife (played by Debra Jo Rupp). Ross and Rachel briefly reconcile in the premiere but soon break up again. Mid-season, having moved on, Ross begins dating an English woman called Emily (played by Helen Baxendale) and the finale, featuring the wedding of the characters, was filmed on location in London. Chandler and Monica sleep together when, after a wedding guest mistakes Monica for Ross' mother, Monica seeks comfort in the arms of a friend. Rachel attends the wedding at the last minute, intending to tell Ross that she still loves him, but she is sidetracked when Ross replaces Emily's name with Rachel's while saying his vows.
The fifth season follows Monica and Chandler keeping their new relationship a secret from their friends, while Ross' marriage to Emily ends before it even started, following their wedding (Baxendale's pregnancy prevented her from appearing on-screen in all but two episodes). Monica and Chandler's relationship becomes public and on a trip to Las Vegas, they decide to get married. On a cliffhanger, 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, although Ross is reluctant to do so, the two get a divorce (Ross's third). Monica and Chandler move into her apartment together and Rachel moves in with Phoebe. Joey, still a struggling actor, gets a part 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 a student (played by Alexandra Holden). Bruce Willis makes a three-episode cameo as her father. Phoebe and Rachel's apartment has a fire meaning Rachel moves in with Joey and Phoebe with Chandler and Monica. In the final episodes, Chandler decides to propose to Monica. Trying to make it a surprise, he starts acting like his old commitment-phobic self, telling her he opposes marriage. For a brief moment Monica considers going to back to Richard, who confesses to her that he still loves her and is willing to have children with her. Monica gets wind of Chandler's idea, and attempts to propose to him but breaks down in tears and cannot finish. Chandler then asks her to marry him and the show is ended with celebration with many of the friends who were standing outside the door.
Season seven largely concerns various wedding-related antics by Monica and Chandler. Joey's television series is cancelled but he is offered his old job back on Days of Our Lives. Phoebe's apartment is fixed but due to the way the apartment has been rebuilt, Rachel stays with Joey. The two-part season finale follows Monica and Chandler's wedding, with guest stars that include Kathleen Turner as Chandler's transvestite father. The closing moments of the season reveal that Rachel is pregnant.
The eighth season's first episodes follow a "Who's the father?" format, with the father revealed to be Ross in episode two and Rachel telling him in episode three. Joey begins to develop romantic feelings for roommate Rachel (who moved in with Joey after a fire at Phoebe's apartment left them with only one bedroom) and when Joey's feelings are revealed things become awkward for the two. Eventually their friendship returns to its status quo but in the finale, following Rachel's giving birth to a daughter, she accepts an accidental proposal of marriage from him. The season was regarded as a return to form for the series; its ratings increased as viewers tuned in for comfort following the September 11, 2001 terrorist attacks. It won the Primetime Emmy Award for Outstanding Comedy Series.
The ninth season follows Ross and Rachel living together with baby Emma after she and Joey clear up the misdirected proposal. She soon moves back in with Joey after a fight with Ross. Monica and Chandler, inspired by Ross and Rachel, decide to conceive a child of their own. They seek medical advice after several episodes of trying for a baby, and discover that both of them are physically unable to conceive. Paul Rudd appears in the recurring role of Mike Hannigan, a new boyfriend for Phoebe. Hank Azaria returns as David "the scientist guy", a character originated in the first season, and Phoebe must choose between the two in a touching finale, deciding to choose Mike. The finale is set in Barbados, where the group goes to hear Ross give a keynote speech at a Paleontologist conference. Aisha Tyler appears as the series' first recurring black character. Tyler plays Charlie, Joey's intelligent girlfriend.
The tenth season closes up several storylines; Monica and Chandler decide to adopt a child, and meet Erica, a birth mother from Ohio (played by Anna Faris). Erica gives birth to twins in the series finale. Phoebe and Mike get married towards the end of the season and Rachel takes a job based in Paris. Ross declares his love for her and they resume their relationship (not making any mistakes this time) in the season finale, while Monica and Chandler move out of their apartment into the suburbs. Joey is upset that everything is changing. Rachel still gets on the plane even with Ross' confessions, but later appears at his apartment door admitting she loves him too. In the series finale, at the end, a tearful Rachel says 'Shall we go get some coffee?' to which Chandler sarcastically responds, 'Sure. Where?' (the last words spoken on the show).