In a garret.
It is Christmas Eve. From the garret window Rodolfo gazes at the snow-covered rooftops of Paris, while Marcello works on a painting. Numb with cold, Rodolfo curses the dismal fireplace («Nei cieli bigi»). Marcello suggests they warm it up by sacrificing a chair, but Rodolfo prefers to burn the manuscript of the tragedy he is working on. When Colline enters, he too tries to warm himself by the ashes of the fire. After a while, however, Schaunard arrives with food, firewood, cigars and wine, which he has received in payment from a rich English lord.

The four friends decide to celebrate in the Latin Quarter. There is a knock at the door. Benoît, their landlord, has come to collect the rent. The four welcome him in, ply him with drink and flattery until, pretending to be scandalised by his amorous adventures, they send him packing. Marcello, Schaunard and Colline go out, while Rodolfo, who has to finish an article, lingers in the room. A timid knock is heard at the door and Mimì, their neighbour, comes in. Her candle has gone out. Seeing her gasping for breath after climbing the stairs, Rodolfo offers her a seat and a drop of wine, as he contemplates her pallid face.

Having regained some strength, Mimì is about to leave the attic when she realises she has dropped the key to her room. Rodolfo helps her look for it, but when he finds it he slips it into hispocket, so that the girl will stay with him a little longer. He takes her hand («Che gelida manina») and briefly tells her his story. He is a poor poet who scrapes a living. Mimì replies by recounting her own life («Mi chiamano Mimì») and confiding her dreams to him. Rodolfo kisses her («O soave fanciulla») and offers her his arm as they go off to the Latin Quarter.