Comedian Alvy Singer is trying to understand why his relationship with Annie Hall ended a year ago. Growing up in Brooklyn, he vexed his mother with impossible questions about the emptiness of existence, but he was precocious about his innocent sexual curiosity, suddenly kissing a classmate at six years old and not understanding why she was not keen to reciprocate.
Annie and Alvy, in a line for The Sorrow and the Pity, overhear another man deriding the work of Federico Fellini and Marshall McLuhan. Alvy imagines McLuhan himself stepping in at his invitation to criticize the man's comprehension. That night, Annie shows no interest in sex with Alvy. Instead, they discuss his first wife, whose ardor gave him no pleasure. His second marriage was to a New York writer who did not like sports and was unable to reach orgasm.
With Annie, it is different. The two of them have fun cooking a meal of boiled lobster together. He teases her about the unusual men in her past. They had met playing tennis doubles with friends. Following the game, awkward small talk leads her to offer him a ride uptown, and then a glass of wine on her balcony. There, what seemed a mild exchange of trivial personal data is revealed in "mental subtitles" as an escalating flirtation. Their first date follows Annie's singing audition for a nightclub ("It Had to be You"). After their lovemaking that night, Alvy is "a wreck," while Annie relaxes with a joint.
Soon, Annie admits she loves Alvy, while he buys her books on death and says that his feelings for her are more than just love. When Annie moves in with him, things become very tense. Eventually, Alvy finds her arm-in-arm with one of her college professors, and the two begin to argue about whether this is the "flexibility" they had discussed. They eventually break up, and he searches for the truth of relationships, asking strangers on the street about the nature of love, questioning his formative years, and imagining a cartoon version of himself arguing with a cartoon Annie portrayed as the Evil Queen in Snow White.
Alvy attempts a return to dating, but the effort is marred by neurosis and an episode of bad sex that is interrupted when Annie calls in the middle of the night, insisting that he come over immediately to kill two spiders in her bathroom. A reconciliation follows, coupled with a vow to stay together, come what may. However, their separate discussions with their therapists make it evident there is an unspoken and unbridgeable divide. When Alvy accepts an offer to present an award on television, they travel to Los Angeles with Alvy's friend Rob. However, on the return trip, they agree that their relationship is not working. After losing Annie to her record producer Tony Lacey, Alvy unsuccessfully tries rekindling the flame with a marriage proposal. Back in New York, he stages a play of their relationship, but he changes the ending: now she accepts.
The last meeting between Annie and Alvy is a wistful coda on Manhattan's Upper West Side after they have both moved on to someone new. Alvy's voice returns with a summation: love is essential, especially if it is neurotic. Annie sings "Seems Like Old Times," and the credits roll.
