A crisis develops in the Oblonsky household when Dolly finds out about her husband's affair. Stiva's sister, Anna Karenina, arrives to reconcile the couple and dissuades Dolly from getting a divorce. Konstantin Levin, Stiva's friend, arrives in Moscow to propose to the eighteen year old Kitty Shtcherbatsky. She refuses him, for she loves Count Vronsky, a dashing army officer who has no intentions of marrying.
Meeting the lovely Madame Karenina, Vronsky falls in love and begins to pursue her. He and Anna are so involved with each other at the grand ball that Kitty's hopes for Vronsky are shattered. Anna, followed by Vronsky, returns to her husband and son in St. Petersburg, while the disappointed Levin returns to his country estate.
Kitty falls ill after her humiliating rejection by Vronsky. At the German spa where she takes a rest cure she tries to deny her womanly nature by becoming a religious do-gooder. Realizing the hypocrisy of this new calling, Kitty returns to Russia cured of her depression and ready to accept her ultimate wifehood.
Consummating her union with Vronsky, Anna steps into a new life with much foreboding for the future. By the time she confesses her adultery to the suspecting Karenin, she is already pregnant with Vronsky's child.
Devoting himself to farming, Levin tries to find life meaningful without marriage. He expends his energies in devising a cooperative landholding system with his peasants to make the best use of the land. Seeing his brother Nicolai hopelessly ill with tuberculosis, he realizes he has been working to avoid facing the problem of death. He also realizes he will always love Kitty.
Vronsky's career ambitions rival his love, and as he has not chosen between them, he is still uncommitted to Anna. Having rejected her husband, but still unable to depend on Vronsky, Anna finds her situation desperate. Her life is in a state of suspension.
Kitty and Levin are engaged to marry. Karenin, who has tried to maintain appearances of domestic tranquillity, finally builds up enough anger to hire a divorce lawyer. Anna is confined of a daughter, but dangerously ill from puerperal fever. At her deathbed, Karenin forgives her and feels sanctified by this surge of humanity and Christian charity. At this sudden reversal of their roles Vronsky feels so humiliated he attempts suicide. These incidents form the turning point of the novel. After Anna's recovery, the lovers go abroad and Anna refuses divorce (though Karenin agrees to it) for fear of giving up her son.
Levin and Kitty, after some initial difficulties, adjust to being married. Nicolai's death affects Levin deeply, and he realizes that emotional commitment, not reason, enables one to overcome life's problems. As if to underscore his life-affirmation, they learn Kitty is pregnant.
After they honeymoon in Italy, Anna and Vronsky return to Petersburg. Violently affected from seeing her son again, Anna's love for Vronsky becomes more desperate now that she has no one else. Despite his objections, she boldly attends the theater as if to affirm her love before conventional society. Humiliated at the opera, she blames Vronsky for lacking sympathy with her suffering, while he is angry at her indiscretion. This keynotes the decline of their relationship, although it is temporarily restored as they go to live in the country.
Among Levin's summer visitors is a socialite who pays so much attention to Kitty that Levin asks him to leave. Visiting Anna at Vronsky's estate, Dolly finds her own drab life preferable to the formal luxury and decadence of Anna's. Complaining that Vronsky is eager for independence, Anna tells Dolly she must rely on her beauty and her love to keep his interest. Vronsky feels especially burdened by the demands of Anna's love when she calls him home from a refreshing political convention.
Kitty gives birth to a son. Karenin, under the influence of his fanatically devout friend, Countess Lydia Ivanovna, becomes religious and uses his hypocritical faith as a crutch to overcome his humiliation and loneliness.
Anna, seeing the irreversible decline of her love affair, has no more will to live and commits suicide.
Vronsky volunteers for service in the Russo-Turkish war. Tolstoy uses this part of the novel to express his pacifist principles. Levin discovers salvation" when he resolves to "live for his soul" rather than for selfish goals. He realizes the meaning of life consists in living according to the goodness inherent in every individual. Understanding death as part of a reality-oriented life, Levin is at peace with himself.