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Infernal Affairs
Theatrical release poster
Traditional Chinese	無間道
Simplified Chinese	无间道
Directed by	Andrew Lau Alan Mak
Written by	Alan Mak Felix Chong
Produced by	Andrew Lau
Starring	Andy Lau Tony Leung Anthony Wong Eric Tsang
Cinematography	Andrew Lau Lai Yiu-fai
Edited by	Danny Pang Curran Pang
Music by	Chan Kwong-wing
Production companies	Media Asia Films Basic Pictures
Distributed by	Media Asia Distribution
Release date	12 December 2002 (2002-12-12)
Running time	101 minutes
Country	Hong Kong
Language	Cantonese
Budget	HK$20 million[1]
Box office	HK$55.1 million

Infernal Affairs (traditional Chinese: 無間道; simplified Chinese: 无间道; lit. 'Unceasing Path') is a 2002 Hong Kong crime drama film^[2] directed by Andrew Lau and Alan Mak from a screenplay written by Mak and Felix Chong. The film stars Andy Lau, Tony Leung, Anthony Wong, and Eric Tsang. The film follows an undercover Hong Kong Police Force officer who infiltrates a triad and another police officer who is secretly a spy for the same triad. The film is the first in the Infernal Affairs series, followed by Infernal Affairs II and Infernal Affairs III (both 2003).

At the 22nd Hong Kong Film Awards, Infernal Affairs won seven out of the sixteen awards it was nominated for—including Best Film, Best Director, Best Actor (Leung), and Best Supporting Actor (Wong). It also won in those categories at the 40th Golden Horse Awards and 8th Golden Bauhinia Awards. The film was selected as Hong Kong's entry for the Best Foreign Language Film at the 76th Academy Awards but was not nominated. Miramax Films acquired the United States distribution rights and gave it a limited American theatrical release in 2004.

American director Martin Scorsese remade the film in 2006 as The Departed, which won the Academy Award for Best Picture as well as Academy Award for Best Director, Scorsese's first and only Oscar in his career, and Best Adapted Screenplay.^[3][4] The film has also been remade in India as Homam (2008), in South Korea as City of Damnation (2009), and in Japan as Double Face [ja] (2012). In 2018, a television series adaptation aired on TVB.