In the attic apartment he shares with friends in the Latin Quarter of Paris, the poet Rodolfo stares out the garret window as the artist Marcello paints. They grouse about the cold and burn the manuscript of Rodolfo's play in their stove for heat. Then the philosopher Colline returns, followed by the musician Schaunard—who, having managed to buy food, wine, and cigars after an unexpected job, is jubilant. Their landlord arrives to collect the rent, but is thwarted when a combination of wine, flattery, and confusing banter sends him packing without the money he's owed; the friends will divide it for a Christmas Eve outing at the Cafe Momus downstairs. Remaining alone in their apartment as his friends leave, Rodolfo hears a knock: it’s their neighbor Mimi, whose candle has blown out. In the few moments it takes for her to lose her key, both lose their hearts and exchange life stories. The frail Mimi coughs and at first demurs to join Rodolfo. But as the act ends they descend the stairs together, ecstatically singing of their new-found love on their way to the cafe.
Act II
Christmas Eve at the Cafe Momus is a boisterous affair. Rodolfo buys a bonnet from a vendor for Mimi while Colline buys a coat and Schaunard a horn. The street bustles with children and celebrants. Musetta, a flamboyant flirt who is Marcello's ex, arrives on the arm of the doddering, wealthy Alcindoro, whom she torments and manipulates by turns. She sends him away to have her suddenlytoo-tight shoe repaired, then rushes into passionate embrace with Marcello. Alcindoro returns just in time to be presented with the bill for all the festivities he's missed. This joyful outing is perhaps the greatest happiness that these six friends will ever know together.
Act III
Two months have passed, and it is a cold February morning at an entry point into the city. Wracked by coughing, Mimi searches for Marcello, who currently lives near the gate at a tavern where he works as a signpainter. Mimi confides to him that despite the love that she and Rodolfo share, she is tormented by his jealousy. But then Rodolfo confides—and Mimi overhears—his fears over her worsening health; his jealousy is a ruse that he hopes will push her toward a wealthier lover who can take better care of her. They resolve to separate "senza rancor," without bitterness. But then, unable to bear parting, they resolve to remain together until spring. Their non-farewell provides a musical foil for the bickering of Marcello and Musetta, who cannot live with each other or without each other.
Act IV
Back in their garret apartment, Marcello and Rodolfo are trying to ply their respective arts, but they have women on their minds: Mimi and Musetta have left them for wealthier men. But then Musetta appears, her former gaiety replaced by seriousness. She is gravely concerned for Mimi, who is weakened by illness and has asked Musetta to bring her to Rodolfo. They help her onto a bed and she briefly feels better, but is near death. Colline leaves to pawn his overcoat for medicine; Rodolfo brings out the bonnet he bought for her on Christmas Eve, which he has kept as a remembrance. The six friends share their last moments of affection with Mimi as her life ebbs away, and the opera ends as Rodolfo helplessly calls her name.