The original idea and inspiration for the film stemmed from a Japanese short story concerning two characters who often walk by each other in a stairwell, but do not converse. In that story the characters end up committing suicide.
During filming, Kar-Wai Wong improvised often with the actors, crafting the story and mood of the film as he went along. Originally, "In the Mood for Love" was a much more obvious romance film, with the actors throwing witty dialog at each other and engaging in several scenes of love-making. Eventually, the actors and director decided to tone the mood down to the more subtle version that was released in theaters.
Director Kar-Wai Wong found the English title for "In the Mood for Love" while listening to a song from a Bryan Ferry CD with a similar title, "I'm in the Mood for Love". It is a cover of a 1930s song with the same title, Kar-Wai Wong used the title and the song in an early Hong Kong trailer of the film, and it was also used in the USA trailer of the film.