12B is a 2001 Indian Tamil-language romantic comedy film written, cinematographed and directed by Jeeva, with dialogues by Sujatha; it is his directorial debut. The film stars Shaam in his debut with Simran and Jyothika in lead roles. Hindi actors Suniel Shetty and Moon Moon Sen play supporting roles, and the music was composed by Harris Jayaraj. The film was released on 28 September 2001 to above-average reviews. Critics praised the new concept but criticised the narrative, which they found confusing.

12B is an unofficial remake of the 1998 British-American romantic drama film Sliding Doors. The film introduced the use of dual narrative to Tamil cinema; it depicts events in a man's life that depend on whether he catches a bus or not. The film gained attention for its casting of Simran and Jyothika, who were two of the leading female actors of Tamil cinema; it is also the first Tamil film in which Shetty and Sen appear.

The dual narrative was later used in the Tamil film Oh My Kadavule (2020).