The early part of season 1 focuses on Ryan Atwood's arrival at Newport Beach after being taken in by Sandy and Kirsten Cohen and the relationships he develops with the residents there. A major theme of the first season is the culture shock Ryan feels as he adjusts to a new life in the high-class society of Newport Beach. He quickly befriends and bonds with Seth Cohen, and begins to have a romantic relationship with Marissa Cooper. He also develops a rivalry with Marissa's then-boyfriend, Luke Ward. However, they eventually become friends when Ryan continues to support Luke in times of trouble. Major conflicts and storylines in season 1 include the love triangle between Seth, Summer, and Anna, Julie and Jimmy Cooper's divorce and its effect on Marissa, conflicts between Ryan and Luke, and the arrivals of Oliver Trask and Theresa Diaz.
The second season of The O.C. continues to follow the tumultuous romantic relationships between Ryan and Marissa, Seth and Summer, as well as Sandy and Kirsten. Josh Schwartz, the show's creator, stated that in season 2, the show would "no longer be about Ryan's past; now it's going to be about Ryan's future" and that this season would "slow down the storytelling a little bit ... and evolve the characters". A number of recurring characters are introduced to cause conflicts, such as D.J., Lindsay Gardner, Zach Stevens, and Alex Kelly, to which the main characters form a variety of relationships. Ryan's brother, Trey Atwood, gets out of jail and also causes problems, such as attempting to rape Marissa, while Sandy and Kirsten face new conflicts that could threaten their marriage. Alan Dale as Caleb Nichol, Kirsten's father, receives star billing this season, and his character dies during it. Also, the Bait Shop becomes a prominent social destination for the teenage characters. Season 2 ends with Marissa shooting Trey after attempting to stop an altercation between him and Ryan.
In the beginning of season 3 Marissa is expelled from the Harbor School and must go to Newport Union, a public high school, for shooting Trey Atwood. There, she meets several new recurring characters, most notably Johnny Harper. Back in Harbor, Taylor Townsend is also introduced as a recurring character. Marissa breaks up with Ryan and becomes romantically involved with Kevin Volchok, a surfer and delinquent high school drop-out. Marissa's younger sister, Kaitlin, also returns to Newport after staying at a boarding school. The Cooper family, left with little money, is forced to move to a trailer. Season 3 ends with the teenage characters' high school graduation and the death of Marissa in a car crash caused by Volchok.
Season 4 begins with the grief the characters experience after the death of Marissa, especially with Ryan, Julie, and Summer. Ryan is coping by cage fighting, and Julie enlists him to find Volchok. Ryan eventually becomes romantically involved with Taylor Townsend, while Seth and Summer face the problems of a long distance relationship as Summer goes off to attend college. Two actors receive star billing this season, Autumn Reeser as Taylor Townsend and Willa Holland as Kaitlin Cooper. By the series finale, Ryan begins college at Berkley and starts his career as an architect, while Summer and Seth get married.
