Wai Ka-fai (born 21 September 1962) is a Hong Kong film director, screenwriter and film producer. Best known for his frequent collaborations with Johnnie To, he co-formed Milkyway Image in 1996, which is now one of the most successful independent film studios in Hong Kong.
The films that Wai and To have made together as directors and producers include Needing You..., Fat Choi Spirit, Love on a Diet, Fulltime Killer, Turn Left, Turn Right, Running on Karma, and Mad Detective. His solo directorial efforts include Too Many Ways to Be No. 1, Written By and Detective vs Sleuths, which the latter helped him won the Hong Kong Film Award for Best Director.
Two of his films were released in the US theatrically: Fulltime Killer and Mad Detective.