12B is a 2001 Indian Tamil-language romance film directed and written by cinematographer Jeeva; it is his directorial debut. The film stars Shaam in his debut with Simran and Jyothika in lead roles. Hindi actors Suniel Shetty and Moonmoon 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.

The plot of 12B is loosely based on 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.

12B introduced the concept of dual narrative to Tamil cinema, which was later used in the Tamil film Oh My Kadavule (2020).