Kareena Kapoor was writer/director Imtiaz Ali's first choice for the role of Geet. Even though he wasn't particularly a fan of hers and hadn't seen her in many movies, he knew she would be able to look natural without makeup, be hyper, talkative and interesting but not irritating.
Kareena Kapoor and Shahid Kapoor who play lovers in the film were also dating in real life - until they broke up whilst making the movie.
Writer/director Imtiaz Ali only settled on Shahid Kapoor for the role of Aditya after meeting him, as he previously viewed him as a "forgettable actor" before realizing that he had "gone through a lot in life and that maturity had never been brought out" and that as such he was perfect for the part of a "young, mature, quiet guy."
The producers had first signed Bobby Deol in 2005. The film had many working titles at the point. "Geet" was one of them. Bobby told the producers to sign Imtiaz Ali because he was very talented .The producers wanted Kareena Kapoor for the film , but Kareena refused to even meet Imtiaz Ali. That is when Bobby suggested they approach Preity Zinta. She agreed but needed six months before she could shoot. This is when Kareena told the producers she would sign the film only if they replaced Bobby Deol with her then boyfriend Shahid Kapoor . The producers agreed and replaced Bobby Deol without even informing him.
Dehli's PVR Cinemas held special screenings of the film on Valentine's Day 2008 to celebrate its 100 days run at the box office.
As part of the film's promotion, the producers painted two full local trains in Mumbai from the Western and Central lines with imagery from the film, with Shahid Kapoor present to chat with fellow passengers and inform them about the movie.
The number of prints for the film across India was increased in its fourth week of release due to popular demand and the lower-than-expected performance of Saawariya (2007).
The title of the film was decided by a popular vote. The other choices were 'Punjab Mail' and 'Ishq Via Bhatinda'.
A private screening of the film was organized at Yash Raj Studios in Mumbai for those associated with the film and their families on October 23rd, 2007.
At one point Bhumika Chawla and Bobby Deol were to head the cast, with the film titled "Train."