Infernal Affairs ( ) is a 2002 Hong Kong crime-thriller film directed by Andrew Lau and Alan Mak. It tells the story of a police officer who infiltrates the crime gang, and a police mole secretly working for the same gang. The Chinese title means "the non-stop path", a reference to Avici, the lowest level of hell in Buddhism. The English title combines the US law enforcement term 'internal affairs' with a reference to Dante's Inferno. Due to its commercial and critical success, Infernal Affairs was followed by a prequel, Infernal Affairs II, and a sequel, Infernal Affairs III, both released in 2003.

Pre-release publicity for Infernal Affairs focused on its star-studded cast (Andy Lau, Tony Leung, Anthony Wong, Eric Tsang, Kelly Chen and Sammi Cheng), but it later received critical acclaim for its original plot and its concise and swift storytelling style. The film did exceptionally well in Hong Kong, where it was considered "a box office miracle" and heralded as a revival of Hong Kong cinema which at the time was considered to be direly lacking in creativity. Miramax Films acquired the United States distribution rights and the film was given a limited US theatrical release in 2004.

The Infernal Affairs series was then remade by Martin Scorsese in 2006 as The Departed, starring Matt Damon, Leonardo DiCaprio, Jack Nicholson and Mark Wahlberg. It went on to receive four Academy Awards, including Best Picture, a Best Director win for Scorcese and Best Adapted Screenplay for William Monahan at the 79th Academy Awards.

Shawn Yue plays a young police officer who has been sent undercover as a mole in the local mafia. Edison Chen plays a young mafia member who is infiltrating the police force. Years later, their older counterparts, Tony Leung and Andy Lau respectively, race against time to expose the mole within their midsts and destroy him. Written by Aya

The setting is the never-ending war between the police and the Triads of Hong Kong. Chan is a cop who's been assigned to undercover work inside the Triads for so long that he's been able to rise through the ranks to a position of some authority. Lau, meanwhile, is a secret member of the Triads who has infiltrated the police force with an equal level of success. As they feed their bosses information on the plans and counter-plans of the organizations they pretend to serve, they both begin to feel the stresses of their double lives as they become torn between the oppressive obligations they owe to their superiors and the growing camaraderie they share with the foot soldiers around them. As the two organizations become increasingly aware of the moles in their midsts, the race is on for Chan and Lau to try and get out of the game alive. Written by Jean-Marc Rocher