Time: around 1920 (1830 in the original).
In the four bohemians' garret
Marcello is painting while Rodolfo gazes out of the window. They complain of the cold. In order to keep warm, they burn the manuscript of Rodolfo's drama. Colline, the philosopher, enters shivering and disgruntled at not having been able to pawn some books. Schaunard, the musician of the group, arrives, announcing: he has earned some money. Tonight they will all celebrate his good fortune by dining at Cafe Momus, and he will pay.
Marcello, Schaunard and Colline go out, but Rodolfo remains alone for a moment in order to finish an article he is writing, promising to join his friends soon. There is a knock at the door. It is a girl who lives in another room in the building. Her candle has blown out, and she has no matches; she asks Rodolfo to light it. She is briefly overcome with faintness, and Rodolfo helps her to a chair and offers her a glass of wine. She thanks him. After a few minutes, she says that she is better and must go. But as she turns to leave, she realizes that she has lost her key.
Her candle goes out in the draught and Rodolfo's candle goes out too; the pair stumble in the dark. Rodolfo, eager to spend time with the girl, to whom he is already attracted, finds the key and pockets it, feigning innocence. He takes her cold hand (Che gelida manina—"What a cold little hand") and tells her of his life as a poet, then asks her to tell him more about her life. The girl says her name is Mimì (Sì, mi chiamano Mimì —"Yes, they call me Mimì"), and describes her simple life as an embroiderer. Impatiently, the waiting friends call Rodolfo. He answers and turns to see Mimì bathed in moonlight (duet, Rodolfo and Mimì: O soave fanciulla—"Oh lovely girl"). They realize that they have fallen in love. Rodolfo suggests remaining at home with Mimì, but she decides to accompany him to the Cafe Momus. As they leave, they sing of their newfound love.
Quartier Latin (same evening)
A great crowd, including children, has gathered with street seller (chorus: Aranci, datteri! Caldi i marroni!—"Oranges, dates! Hot chestnuts!"). The friends arrive; Rodolfo buys Mimì a present.The children of the streets clamor to see the wares of Parpignol, the toy seller.
As the men and Mimì dine at the cafe, Musetta, formerly Marcello's sweetheart, arrives with her rich (and elderly) government minister admirer, Alcindoro, whom she is tormenting. It is clear she has tired of him. To the delight of the Parisians and the embarrassment of her patron, she sings a risqué song (Musetta's waltz: Quando m'en vo'—"When I go along"), hoping to reclaim Marcello's attention. The ploy works; at the same time, Mimì recognizes that Musetta truly loves Marcello. To be rid of Alcindoro for a bit, Musetta pretends to be suffering from a tight shoe and sends him to the shoemaker to get her shoe mended. Alcindoro leaves, and Musetta and Marcello fall rapturously into each other's arms.
The friends are presented with their bill. However, Schaunard's purse has gone missing and no one else has enough money to pay. The sly Musetta has the entire bill charged to Alcindoro. Alcindoro returns with the repaired shoe seeking Musetta. The waiter hands him the bill and, dumbfounded, Alcindoro sinks into a chair.
Mimì appears, coughing violently. She tries to find Marcello. She tells him of her hard life with Rodolfo, who abandoned her the night before, and of Rodolfo's terrible jealousy (O buon Marcello, aiuto!—"Oh, good Marcello, help me!"). Marcello tells her that Rodolfo is asleep inside, and expresses concern about Mimì's cough. Rodolfo wakes up and comes out looking for Marcello. Mimì hides and overhears Rodolfo first telling Marcello that he left Mimì because of her coquettishness, but finally confessing that his jealousy is a sham: he fears she is slowly being consumed by a deadly illness (most likely tuberculosis). Rodolfo, in his poverty, can do little to help Mimì and hopes that his pretended unkindness will inspire her to seek another, wealthier suitor (Marcello, finalmente—"Marcello, finally").
Out of kindness towards Mimì, Marcello tries to silence him, but she has already heard all. Her weeping and coughing reveal her presence, and Rodolfo hurries to her. Musetta's laughter is heard and Marcello goes to find out what has happened. Mimì tells Rodolfo that she is leaving him, and asks that they separate amicably (Mimì: Donde lieta uscì—"From here she happily left"); but their love for one another is too strong for the pair to part. As a compromise, they agree to remain together until the spring, when the world is coming to life again and no one feels truly alone.
Back in the garret (some months later)
Marcello and Rodolfo are trying to work, though they are primarily talking about their girlfriends, who have left them and found wealthy lovers. Rodolfo has seen Musetta in a fine carriage and Marcello has seen Mimì dressed like a queen. The men both express their nostalgia (duet: O Mimì, tu più non torni—"O Mimì, will you not return?"). Schaunard and Colline arrive.
Musetta suddenly appears. Musetta found Mimì that day in the street, severely weakened by her illness, and Mimì begged Musetta to bring her to Rodolfo. Mimì, haggard and pale, is assisted onto a chair. Briefly, she feels as though she is recovering. Musetta and Marcello leave to sell Musetta's earrings in order to buy medicine, and Colline leaves to pawn his overcoat (Vecchia zimarra—"Old coat"). Schaunard leaves with Colline to give Mimì and Rodolfo some time together. Mimì tells Rodolfo that her love for him is her whole life (aria/duet, Mimì and Rodolfo: Sono andati?—"Have they gone?").
To Mimì's delight, Rodolfo presents her with the little present, which he has kept as a souvenir of their love. They remember past happiness and their first meeting—the candles, the lost key. Suddenly, Mimì is overwhelmed by a coughing fit. The others return, with a gift of a muff to warm Mimì's hands and some medicine. Mimì gently thanks Rodolfo for the muff, which she believes is a present from him, reassures him that she is better and falls asleep. Musetta prays. Schaunard discovers that Mimì has died. Rodolfo rushes to the chair, calling Mimì's name in anguish, weeping helplessly. Mimì is going away to the light.