The third season, September 8, 2005 - May 18, 2006, contained 25 episodes and ends with the death of Marissa Cooper, one of the main characters of the series. To see music featured during this season, see Season 3 Music.
- The departure of Trey Atwood, who fell into a coma after being shot last season by Marissa Cooper and left Newport Beach on a Greyhound bus to Las Vegas.
- The arrival and departure of Charlotte Morgan, a con artist who tries to manipulate Kirsten Cohen while at rehab. Her plans to steal money from the people of Newport were thwarted by Julie Cooper.
- Julie and Kirsten starting a catering business, then later deciding to turn it into a high-end dating service.
- Marissa being expelled from The Harbor School for shooting Trey. After some help from her friends, Taylor and Sandy, she is readmitted by the school board.
- The arrival and death of Johnny Harper, a former schoolmate of Marissa's while she was at Newport Union. Johnny develops a love for Marissa, for helping him out when he couldn't make the surfing team. Johnny dies from head injuries sustained from a drunken fall off of a cliff.
- The introduction of Taylor Townsend, Summer's rival, the two of whom fight over the social chair position previously occupied by Marissa. Later, however, she becomes a friend of Seth and Summer, when the two realize how much her mother is bad with her.
- The arrival and departure of Jack Hess, the new Dean of Discipline, who leaves after Summer finds out about his relationship with Taylor and blackmails him to let Ryan back in Harbor.
- The return and then the final goodbye by Jimmy Cooper, who was deep in debt with a loanshark named Don. Jimmy eventually fails to pay back the money and as a result, he is severely beaten by Don and his cronies. Jimmy originally plans to marry Julie for her inheritance, but leaves after discovering that Caleb was bankrupt.
- Julie and Marissa are evicted from the mansion. Julie hits rock bottom as she is forced to live out of a low-rent motel room, while Marissa moves in with Summer. Julie eventually abandons her motel room for a trailer park.
- Sandy taking over control of the Newport Group, and hiring newcomer Matt Ramsey to help run it.
- Seth, Ryan, Summer and Marissa applying for college ; Seth and Summer to Brown, Ryan and Marissa to University of California, Berkeley.
- The return of Kaitlin Cooper from boarding school for the holidays. She is more rebellious and devious than before; it is revealed that she stole money to go back home, smokes marijuana, and sparked more trouble in the Ryan-Marissa-Johnny love triangle. She decides to leave after her classmate starts a new relationship with her during Valentine's Day.
- Seth starts to smoke marijuana, which was supplied by Kaitlin, to relieve college pressures. He ends up skipping his interview with a Brown University scout. Summer discovers this, and she arranges for a second interview for him.
- Ryan and Marissa deciding to break up, after the complications surrounding Johnny's death.
- The arrival and departure of Sadie Campbell, Johnny's cousin, who moved from Oregon to help Johnny's mother. Ryan falls for her during a road trip to find Johnny's dad and obtain money from his child support. Ryan's future depature for college left Sadie no choice but to leave Newport Beach.
- The arrival and departure of Matt Ramsey, Sandy's assistant in running the Newport Group. His personal life conflicts with his job, notably when he was temporarily fired for taking Ryan to a strip club, screwing up a presentation for a project, and dating a board member's (Henry Griffin) daughter in order to persuade him on doing the hospital project. He was fired by Sandy after Griffin gave him an ultimatum to either fire Matt or leave the hospital project. He attempts to blackmail Griffin with evidence of his corruption, which backfires. Sandy intervenes to protect Matt, who leaves for Chicago to start his own business with a severence check given by Sandy.
- The introduction of Kevin Volchok, a surfer who was Johnny's rival. He had an affair with Johnny's ex-girlfriend and it was apparent that he and Sadie Campbell had a relationship. Later, after Ryan and Marissa break up, he begins a relationship with Marissa, as part of a downward spiral with her alcohol relapse and experimenting with cocaine.
- The return of Dr. Neil Roberts, Summer's father. He started to develop a loving relationship with Julie Cooper, after a conversation during the Chrismukkah season. They soon leave for a cruise, and when they return, are engaged.
- Ryan and Marissa are accepted to the Berkeley. Summer gets into Brown University. However, Seth is rejected by Brown. He doesn't want to ruin her future, as she earlier promised that if he didn't get in, she wouldn't go to Brown, to stay with him. He decides to break up with Summer by telling her that he "doesn't love her anymore."
- The return of Dawn Atwood, who is found in jail by Sandy for Ryan's 18th birthday. She leaves Ryan a note, rather than accompanying Sandy back to Newport Beach for the party. Later, Ryan travels to see her and invite her to graduation, where he meets, and has a one night stand with, his mother's co-worker, Chloe.
- Ryan discovers that Theresa didn't lose the baby, but also that it isn't his. Her son, Daniel, was fathered by former boyfriend Eddie.
- The return of Anna Stern, who meets Seth at a Brown University orientation tour. She helps Seth with his college problems by getting him an interview at the Rhode Island School of Design.
- Kirsten relapsing and drinking a glass of wine, after being frustrated by Sandy's devotion to the Hospital project.
- The Senior Prom. Ryan takes Theresa, Seth takes Anna, who is still on a mission to help get back Summer, Marissa takes Volchok, and Summer takes a Korean K-Pop star, Yung Nom. At the prom, Summer gets drunk, while Volchok cheats on Marissa and steals Taylor's prom funds. At the end of the evening, Seth finally tells Summer the whole truth, and they reunite.
- Sandy being told by Dr. Roberts that he would be under investigation over his dealings with Henry Griffin, after which Sandy decides to assist the district attorney's office in their investigation.
- A fight between Ryan and Volchok after Ryan learns that he stole Taylor's prom funds, leaving Volchok unconscious and with broken ribs. Volchok then blackmails Ryan into helping him pick up something, and Ryan agrees until he finds out that Volchok is stealing a car.
- Seth leaving a lit marijuana cigarette in Sandy's office at the Newport Group Office. The office caught fire and Seth was arrested shortly afterwards.
- Sandy's refusal to accept the "Riviera Magazine Man of the Year" award on the grounds that he will fully cooperate with the district attorney's office in their investigation of Henry Griffin and his misdeeds in the construction of the hospital, and to spend more time with his family.
- The death in the last episode of the season, by Marissa Cooper, one of the main characters in the series, which was caused by Volchok.
- Peter Gallagher as Sandy Cohen
- Kelly Rowan as Kirsten Cohen
- Benjamin McKenzie as Ryan Atwood
- Adam Brody as Seth Cohen
- Mischa Barton as Marissa Cooper
- Melinda Clarke as Julie Cooper
- Rachel Bilson as Summer Roberts
Although Tate Donovan made a few appearances as Jimmy Cooper, he was not credited as part of the main cast for the season. Mischa Barton left the main cast after the death of her character, Marissa Cooper.
|Picture||Title||Episode #||Writer||Episode #|
|The Aftermath||3.01||Josh Schwartz||September 8, 2005|
|It has been a couple of months since the shooting. Trey has been in a coma all this time leaving the District Attorney impatiently waiting for his side of the story. Feeling the pressure from the community the D.A. continues to put pressure on Ryan, Marissa, Seth, Summer and others for more information. Meanwhile Julie is steaming mad because Caleb’s accountant won’t give up the goods on Caleb’s will and Kirsten is still in rehab.|
|The Shape of Things to Come||3.02||J.J. Philbin||September 15, 2005|
|Social Chair Summer tries to plan this year’s carnival but is having much difficulty due to a little pest named Taylor. Sandy is surprised to find Kirsten has been released from rehab but instead of informing him, she has been living with another woman named Charlotte who she met in rehab. Julie and Sandy meet with the Dean and Dr. Kim to discuss Ryan and Marissa’s future at Harbor High. Later Ryan and Marissa partake in a similar meeting. Elsewhere Jimmy meets a man and feels more than open to discuss his money problems with him.|
|The End of Innocence||3.03||Stephanie Savage||September 22, 2005|
|Jimmy must make once more the difficult decision to leave or stay with his family; Kirsten returns to the Cohen household while Charlotte has to leave her house; Marissa and Ryan face a possible separation; Taylor lords over the school musical and makes Summer and Seth her stooges.|
|The Last Waltz||3.04||John Stephens||September 29, 2005|
|Marissa begins her first day at Newport Union Public School and Ryan doesn't seem to take a liking to the new friends she's made; Charlotte's true intentions towards Kirsten are revealed; Summer finds out the horrifying truth between the Dean and Taylor; Kirsten has a big decision to make regarding the Company.|
|The Perfect Storm||3.05||Mike Kelley||November 3, 2005|
|Ryan decides to make a life-changing decision that Sandy surprisingly supports, and Marissa turns to her new public school friends for help with Ryan. Meanwhile, Harbor High's Dean of Discipline, Dean Hess, continues his crusade to ruin Ryan's future, and Summer and Seth go on their own crusade to reveal Dean Hess's secret. Meanwhile, Charlotte makes Julie an offer she cannot refuse.|
|The Swells||3.06||J.J. Philbin||November 10, 2005|
|Taylor Townsend locks up Seth's night when she throws a Harbor School event that keeps Summer at a distance. Meanwhile, Marissa's new friendships at public school worry Summer and she enlists Ryan's help. Meanwhile, Sandy works on a plan for the Newport Group and forms a new partnership. And Charlotte convinces Julie and Kirsten to edge back into Newport society.|
|The Anger Management||3.07||John Stephens||November 17, 2005|
|When the gang heads to The Bait Shop to see The Subways, Taylor's horsing around causes a major rift between Seth and Summer. Marissa, determined to end the potentially explosive rift between Ryan and Volchok, does whatever it takes to watch out for Ryan. Meanwhile, Matt, Sandy's Newport Group partner, goes above and beyond the call of duty; Julie Cooper reigns supreme as the only "bitch" in Orange County; and Ryan needs to use his head for once.|
|The Game Plan||3.08||Cory Martin||December 1, 2005|
|As college options are weighed, Seth looks east, Summer west and Taylor looks happy with their possible separation. Ryan, meanwhile, tries to persuade Marissa to go to school at all before Johnny proposes another direction. Elsewhere, Kirsten offers Julie a business opportunity.|
|The Disconnect||3.09||Stephanie Savage||December 8, 2005|
|Ryan takes an internship working for Sandy and Matt at the Newport Group, but he ends up working harder to save Matt's reputation. Summer and Seth, determined to get accepted to Brown University, do whatever it takes to stand out at Harbor School. Johnny finally tells Marissa how he really feels. After Ryan and Marissa cross paths, they end up telling each other the truth.|
|The Chrismukkah Bar Mitz-vahkkah||3.10||Josh Schwartz||December 15, 2005|
|After the gang spends hours picking out the perfect Christmas trees, they devise a special plan to help a friend in need. Meanwhile, the holidays bring out a somber Summer who misses her mom, and Johnny's sudden misfortune forces him to take matters into his own hands. Kirsten, meanwhile, puts the past behind her and reaches out to Julie Cooper. And when a reminiscing Seth vows to put a little "mukkah" into Ryan's "Chris," Ryan gets Bar-Mitz-vahkkahed on the third annual O.C. "Chrismukkah" episode.|
|The Safe Harbor||3.11||Mike Kelley||January 12, 2006|
|Summer, Seth and Ryan launch a mission-impossible campaign to get Marissa back into Harbor, and Johnny struggles between a friend's happiness and his own feelings. Meanwhile, Sandy must make an ethical decision that could change Marissa's fate, and Julie Cooper and Dr. Roberts are apprehensive about admitting to the lies they have told their daughters.|
|The Sister Act||3.12||Leila Gerstein||January 19, 2006|
|Kaitlin Cooper, returns to the O.C. during her winter break from an exclusive Montecito boarding school, bringing a lot of attitude and a few secrets of her own. Much more in the mold of her mother Julie Cooper than her sister Marissa, Kaitlin turns heads as she tries to get closer to her family the only way she knows how.|
|The Pot Stirrer||3.13||John Stephens||January 26, 2006|
|While Marissa does all she can to get to know her sister, Kaitlin just stirs up trouble for the gang as she prepares to celebrate her birthday. Sandy encourages Seth about college, but Seth finds a better alternative. Sandy and Matt work together to secure a contract for the new hospital. And Julie continues her quest to put her family back together again.|
|The Cliffhanger||3.14||J.J. Philbin||February 2, 2006|
|Summer discovers the truth about Cohen, while Sandy and Matt encounter an obstacle with their hospital project. Meanwhile, Kirsten and Julie take their matchmaking business a little too far, causing Julie to go into hiding. Marissa finally tells Johnny how she truly feels and Kaitlin wonders which "Cooper" Johnny really likes. When Johnny and Kaitlin head to the beach, Kaitlin finds Johnny at the edge of reason.|
|The Heavy Lifting||3.15||Stephanie Savage||February 9, 2006|
|Tragic news forces the gang to sort out their problems and face the reality of the situation. After Sadie arrives in Newport, Ryan helps her move and get rid of Volchok, causing Ryan to question his and Marissa's relationship. Meanwhile, Kaitlin's winter break is over - just as she gets close to her family, she once again has to say goodbye. Will she ever return to the O.C.? And in the wake of Newport's latest events, Kirsten and Julie press on with their Valentine's Day party.|
|The Road Warrior||3.16||Mike Kelley||March 9, 2006|
|Summer asks Julie and Kirsten, via their matchmaking company, to find a woman for her father. Ryan helps Sadie find her trouble-ridden uncle Jack, and Sadie wants to collect. Marissa is yet again involved in another police investigation, and she and Ryan break up.|
|The Journey||3.17||John Stephens||March 16, 2006|
|Summer and Julie talk about the latter's relationship with Dr. Roberts. Sandy goes to jail to visit Dawn Atwood. Volchok insists a little too much to have a talk with Marissa. Matt comes to her rescue. Later, she decides not to go to Ryan's birthday party, goes to the beach and rings Volchok, to talk to him. The episode ends with Marissa resting her head on Volchok's shoulder.|
|The Undertow||3.18||Mark Fish & J.J. Philbin||March 23, 2006|
|Ryan has problems opening up to Sadie. Henry Griffin drops by the Newport Group and wants to talk to Sandy about problems with Matt's personal life. Taylor helps Seth and Summer deal with their couple problems. Marissa shows weakness towards Volchok, and one thing leads to another.|
|The Secrets and Lies||3.19||Stephanie Savage & Josh Schwartz||March 30, 2006|
|Julie and Dr. Roberts announce their engagement; Marissa seeks solace with some bad company. Ryan tries to move on with Sadie, Kirsten surprises Seth with a night out, and Sandy's woes with Matt continue.|
|The Day After Tomorrow||3.20||Leila Gerstein||April 6, 2006|
|The college acceptance and rejection letters arrive leaving the kids to consider their future. Taylor organises a college bonfire party ; Summer and Marissa fix their problems. Seth tells Summer she should go to brown but he will go elswhere causing them to break up|
|The Dawn Patrol||3.21||Mike Kelley||April 13, 2006|
|Ryan visits his mother but there's a problem. Taylor and Summer aim to find out Seth's secret. Julie helps Marissa out of a bad situation. Sandy solves his work problems but hurts Kirsten in the process.|
|The College Try||3.22||J.J. Philbin||April 20, 2006|
|Graduation is just weeks away and Ryan, Seth, Summer and Marissa leave Newport to attend their respective pre-frosh orientations at UC Berkeley and Brown. Kirsten is suprised by who she sees at the airport. Seth is suprised by who he meets at Brown. Later, Sandy and Kirsten attend a hospital benefit where Kirsten returns to an old habit.|
|The Party Favor||3.23||John Stephens||April 27, 2006|
|Taylor hits a high at prom, while Summer falls flat with her date. Seth and Anna plan to win Summer back. Marissa convinces Volchok to go to the prom and Ryan brings an unexpected old flame. When one of the girls is elected prom queen, it truly becomes a night to remember. Later, Taylor's prom funds are missing and Ryan returns to his old ways.|
|The Man of The Year||3.24||Stephanie Savage||May 4, 2006|
|Ryan and Volchok make a deal. Sandy is named Man of The Year. Marissa goes to visit Kaitlin at boarding school. Meanwhile, Theresa has to make a difficult decision.|
|The Graduates||3.25||Bob DeLaurentus & Josh Schwartz||May 18, 2006|
|After the graduation ceremonies Ryan has to face Volchok's threat. Merissa decides to help Ryan, because without her, he would have never been dragged into the problems with her recent affair. Although they pay off Volchok, season 3 ends tragically.|