Anna Karenina opens at the Oblonsky household in Moscow. Dolly has caught her husband, Stiva (a.k.a. Stephen; Stiva's his nickname) cheating, and now she's threatening to leave him. Stiva Oblonsky's sister, Anna Karenina, wife of Alexis (or Alexei) Karenin, is taking a train from Petersburg to act as a marriage counselor.
Anna arrives at the train station with an elderly woman named Countess Vronsky, whose son, Alexis (or Alexei) Vronsky is immediately smitten with Anna. (It is confusing that both Karenin, Anna's husband, and Vronsky are named Alexis. This is where patronymics come in handy: Vronsky is Alexis Kirillovich and Karenin is Alexis Alexandrovich.) Before the group leaves the station, a drunken guard is crushed to death underneath the train. In an effort to impress Anna, Vronsky gives money to the man's widow.
There are a few obstacles to Vronsky and Anna's courtship. First of all, as we have already said, Anna is a married woman. What's more, she has an eight-year-old son, Seryozha (a.k.a. Sergei; Seryozha is his nickname). And to make matters even worse, Vronsky is already courting Dolly Oblonsky's sister, Kitty.
Anna succeeds in reconciling the Oblonskys, and Kitty and Anna become friends. Constantine Levin, who is good friends with Stiva Oblonsky, comes to Moscow to propose to Kitty. But Kitty rejects him because she's in love with Vronsky. So Levin runs back to the country, where he feels most at home.
After Kitty has refused Levin in favor of Vronsky, she goes to a ball (along with everyone in Moscow) where her heart is broken by Vronsky. Much to everyone's surprise, Vronsky neglects Kitty in favor of Anna. Having saved her brother's marriage, Anna leaves for Petersburg the next day. When Anna takes a break during the train ride, she bumps into Vronsky. He's following her from Moscow to Petersburg.
Once Vronsky turns his romantic attention to Anna, Kitty falls ill. Her treatment is to go abroad and visit a German spa with her mother. Meanwhile, in Petersburg, Vronsky continues to pursue Anna. Resisting the temptation of an affair, Anna begs Vronsky to reconcile with Kitty, but Vronsky replies that he is in love with Anna.
The same night, Karenin (Anna's husband) finally suspects that something's up and tries to talk to Anna about the nature of her relationship with Vronsky. She dodges all his questions. After this night, Anna and Karenin's marriage has irrevocably altered. Anna sees Vronsky everywhere, and the two of them begin an affair. Anna is filled with guilt.
Meanwhile, back in the country, Levin is still languishing over Kitty. Oblonsky (brother to Anna and brother-in-law of Kitty) goes to visit Levin. And in Petersburg, everyone who knows of it has turned against the affair between Anna and Vronsky. Vronsky's mother condemns the affair because she thinks her son's infatuation with Anna is interfering with his military career.
Before a horse race in which Vronsky is competing, he goes to visit Anna, who tells him that she's pregnant. During the race, which is attended by both Anna and Karenin, Vronsky makes an error which trips up his horse, breaking its back. Anna freaks out at Vronsky's accident, and Karenin leads her away. Anna's intense reaction to Vronsky's accident irritates Karenin's suspicions, and during their carriage ride home, Anna blurts out everything. Karenin asks Anna to maintain appearances while he figures out how he wants to respond.
At the German spa, Kitty meets Levin's consumptive brother Nicholas (a.k.a. Nicolai) and befriends a generous young woman named Varenka. Kitty tries to emulate Varenka's example of living for others by caring for a number of different invalids. This plan backfires on Kitty when an impoverished painter falls in love with her. The arrival of Kitty's father helps Kitty see her new activities in a more realistic light. Having gotten over Vronsky, Kitty returns to Moscow, and Varenka promises to visit after Kitty gets married.
Levin's half-brother, Koznyshev, goes to visit Levin for the summer. Koznyshev is a well-known writer and intellectual who criticizes Levin for leaving his administrative duties at the local council. Frustrated with the bureaucracy of the local council, Levin instead pushes for agricultural innovations on his own estate.
Dolly and her children (remember the Oblonskys from the first chapter? Dolly is Anna's sister-in-law and Kitty's older sister) are also in the country, on an estate close to Levin's. The two visit each other, and Dolly makes it clear to Levin that he should propose again to Kitty. Although Kitty visits Dolly in the country, Levin completely avoids the sisters. Instead, he throws himself into farm work.
Back in Petersburg, Karenin wants to keep up appearances and he also doesn't want to make life easier for Anna and Vronsky, so he refuses Anna's request for a divorce. He writes to her, asking her to repent and return to Petersburg (they've been living separately). Meanwhile, Anna is confused. She hasn't told Vronsky that she has confessed everything to her husband. She decides to take her son and flee to Moscow. Karenin's letter arrives and Anna realizes that she doesn't have the strength to abandon her position. She feels desperate to see Vronsky and manages to engineer a meeting. The meeting is fruitless; both of them misunderstand each other. Anna leaves for Petersburg, where her husband tells her she can't receive Vronsky at home, nor give society or the servants cause to gossip about her.
Locked in her empty sham of a marriage to Karenin, Anna heads off to the family's country estate, where she and Vronsky continue their affair. Everything becomes even more complicated and awkward when Anna reveals to Karenin that she's pregnant. And it really hits the fan when Karenin catches Vronsky in the front hallway of their country home. The next morning, Karenin ransacks Anna's desk, finds Vronsky's letters to her, and then consults a lawyer about getting a divorce.
Karenin prepares for a business trip out to several remote provinces of Russia, but he stops in Moscow first, where the Oblonskys insist that he come to their dinner party. It's a fabulous night, although it turns sour for Karenin at the end. Dolly begs him not to divorce Anna: it would make her a social outcast. But this just makes Karenin more determined to end his marriage. While Karenin is busy being bitter, Levin and Kitty are extremely affectionate with one another. After dinner, Levin proposes to Kitty. She finally says yes.
Before Karenin leaves Moscow, he receives a note from Anna saying that she's dying and requesting him to come to her bedside. When he arrives, Anna's baby girl has already been born, but Anna is deathly ill. At her delirious insistence, Karenin forgives both Anna and Vronsky and tells Anna that he'll give her a divorce after all. Vronsky and Anna decide not to take the divorce, but they do drop everything and head to Europe together, leaving Karenin alone.
Kitty and Levin get married, despite last-minute doubts. After three months with Kitty, Levin realizes that marriage is not what he expected, but he and Kitty are in love and slowly learning how to function as a couple. The two of them go to take care of Nicholas (Levin's brother) on his deathbed. Towards the end of their stay, Kitty learns she is pregnant.
Back in Petersburg, Karenin turns out to be pretty bad at coping on his own. Luckily for him, a woman named Countess Lydia is in love with Karenin, and she's more than willing to help him out. Lydia tells Seryozha (Anna's eight-year-old son) that his mother is dead, but Seryozha doesn't believe it.
When Anna writes asking to see her son, Countess Lydia convinces Karenin that this is a bad idea. Anna shows up on Seryozha's birthday anyway and has a joyful reunion with her boy. But this creates tension between Anna and Vronsky: Anna refuses to talk to Vronsky about missing her son, but at the same time she blames Vronsky for letting her suffer alone. In fact, she's getting increasingly resentful of the fact that Vronsky can still move around in society, while their affair has made Anna an outcast. She gets so upset by her outsider status that she and Vronsky immediately head back to the country
Speaking of the countryside, Levin's house in the country has been invaded by guests: Dolly (his sister-in-law) and her children, Varenka (remember that lady Kitty admired so much at the German spa?), Kitty's mother, and Koznyshev (Levin's intellectual brother) are all staying with Levin and Kitty.
When Oblonsky comes for a visit, he brings a man named Veslovsky, who brings news of Anna and Vronsky. Apparently, the couple is living about fifty miles from Levin. Dolly intends to visit Anna. Veslovsky's stay with the Levins does not last long, however, as he flirts with Kitty. In a jealous rage, Levin kicks the guy out of his house.
When Dolly goes to visit Anna, she feels uncomfortable throughout her stay. Everything at the house is new, foreign, and expensive. Vronsky asks Dolly to talk to Anna about obtaining a divorce from Karenin in order to formalize their position as a couple, and give their children some legitimacy. All in all, Dolly is relieved when she gets to go home to her own family.
The more Anna clings to Vronsky, the more he feels like he needs some space. He's very involved in public affairs and has an important role in the elections for Kashin Province. Levin, who's pretty fed up with bureaucracy (after all, he left his own administrative council) attends the same elections, in which the young liberals win.
Towards the end of the election process, Anna pens a letter to Vronsky asking him to come home. He does so immediately. She's convinced that Vronsky's growing tired of her, and finally writes to Karenin to request a divorce. Anna and Vronsky then move to Moscow to settle down as a married couple (except that they're still not actually married. Karenin's slow with the divorce).
The Levins have also moved to Moscow, and their stay drags on as Kitty's pregnancy continues. Levin is not sure how to handle the big city, and he gets sucked into gambling, drinking, and buying expensive things. After a night partying with his buddies, Oblonsky persuades Levin to meet Anna. He promptly falls for her, which does not make his wife, Kitty, happy. The next day, Kitty delivers a healthy baby boy whom they name Dmitri (nicknamed Mitya).
Anna wonders why her charms are failing to work on Vronsky, if it's so easy to seduce upright guys like Levin. She is frustrated because she feels like she has given up everything for Vronsky – her son with Karenin, her position in society – and now he doesn't love her any more.
Oblonsky travels to Petersburg, first, because he wants a job, and second, to speak with Karenin about Anna's divorce. While there, he sees Anna's son, Seryozha. Seryozha has grown into a handsome boy, and has repressed all memories of his mother. Karenin needs to take pity on his estranged wife, Oblonsky argues, because Anna is being destroyed by the long wait for a divorce. Despite Anna's own pitiable emotional state and his own promises, Karenin decides against the divorce.
Anna and Vronsky's relationship is caught in a downward spiral, and Anna becomes increasingly clingy, neurotic, and certain that Vronsky is deliberately delaying his return to the countryside to avoid her. Her desperation ends with her suicide. Having gone to the train station to meet Vronsky, Anna instead throws herself under a train.
The novel resumes almost two months later when Koznyshev visits Levin in the country. He rides the same train as Vronsky, who is going to fight in the Serbian Wars supporting the Slavic cause against the Ottoman Empire. It is obvious that Vronsky views going to war as a quick and easy way to die. He's depressed, and it seems that Anna got her last wish – both to rekindle his love for her and cause him suffering.
Meanwhile, out in the country, Levin continues to struggle with philosophical questions until a local peasant tells him that the purpose of life is "to live not for one's own needs but for God" (8.12.4). As Levin struggles with this message, he has an epiphany that resolves his philosophical battles and affirms his faith in God. This leads him finally to embrace his love for his son and the importance of his domestic life. And that’s the end of Anna Karenina.