Alai Payuthey, also spelled as Alaipayuthey ( transl. Waves are flowing), is a 2000 Indian Tamil-language romantic musical film co-written, co-produced, and directed by Mani Ratnam, starring R. Madhavan and Shalini. The film explores the tensions of married life between two young people who elope and the maturing of love among urban Indians who are conflicted between tradition and modernity. The score and soundtrack were composed by A. R. Rahman.

The film's story is mostly recollected in flashbacks by Karthik (Madhavan), on how he and Shakthi (Shalini) fall in love against the backdrop of Chennai and its suburban trains, against the wishes of their parents. The film had a mostly positive reception by critics.

The film made its European premiere at the Berlin International Film Festival in 2001. It was shown at various film festivals nationally and internationally. It was dubbed and released in Telugu under the title Sakhi. Alai Payuthey was later remade and released in Hindi in 2002, as Saathiya, directed by Shaad Ali.