Infernal Affairs III is a 2003 Hong Kong crime action film directed by Andrew Lau and Alan Mak. It is the third and final installment in the Infernal Affairs film series, and is both a sequel and a semi-prequel to the original film, as it intercuts events before and after the events in the first film. Andy Lau, Tony Leung, Kelly Chen, Anthony Wong, Eric Tsang, and Chapman To reprise their roles again, joined by new cast members Leon Lai and Chen Daoming.

Infernal Affairs III received mixed to positive reviews, grossed $4.5 million and was nominated for seven Hong Kong Film Awards.

There are two cuts of the film, both available on DVD: a 107-minute version which was released in Hong Kong theatres, and a 118-minute version, which is the directors' cut.