In the movie, Jesse (Ethan Hawke) confesses to Celine (Julie Delpy) that he wrote a book about their meeting 9 years before, partially in the hope that she would read it, and re-establish contact with him. Like Before Sunrise (1995), this is based on events in director Richard Linklater's own life. He had once spent a night walking and talking around Philadelphia with a woman called Amy in 1989. Though they initially stayed in touch over the telephone, they lost contact eventually. In 1994, Linklater shot Before Sunrise (1995), based on his night with Amy. Like Jesse in "Before Sunset", Linklater was secretly hoping that Amy had heard of the movie, and would show up at the premiere, but she did not. When "Before Sunset" was released, she did not show up either. It wasn't until 2010, before Linklater started production on the second sequel, Before Midnight (2013), that a friend of Amy, who knew about their story, contacted Linklater to tell him that Amy had died in a motorcycle accident on May 9, 1994, at the age of 24, a few weeks before he started shooting Before Sunrise (1995).
Jesse has married a woman because she became pregnant, and they are now in a wedding crisis. This parallels the story he told in Before Sunrise (1995), about his parents marrying because of his mother's unexpected pregnancy, and their subsequent divorce.
Since the film takes place during the mid-late afternoon, it was the only time of day director Richard Linklater would shoot the scenes in the film. He felt it added to the hyper reality of the film, and often relied on the actors to get perfect takes at the right time.
Jesse is in a failing marriage with a woman he married because she had become pregnant. Soon after the film's release, Ethan Hawke's real-life wife Uma Thurman, whom he had married while she was pregnant with their first child, filed for divorce for adultery.
The film is notable for essentially taking place in real time, i.e. the time elapsed in the story is the run time of the film. In the fast-changing temperate Paris climate, this created challenges for the cinematographer Lee Daniel to match the colour and intensity of the skies and ambient light from scene to scene. The scenes were mostly shot in sequence, as they were still developing the screenplay.
At one point, Jesse reveals that his son's name is Henry, and that he is four years old. When Jesse and Celine get on the boat, he tells the driver to pick him up at "Henry Quatre," which translates to "Henry Four" or, Henry IV.
After the filming of Before Sunrise (1995), Richard Linklater, Ethan Hawke, and Julie Delpy discussed making a sequel. Linklater considered a version to be filmed in four locations and with a much larger budget. When his proposal did not secure funding, he scaled back the concept of the movie. In a 2010 interview, Hawke said that the three had worked on several potential scripts over the years. As time passed and they did not secure funding, they adapted elements of the earlier scripts for Before Sunrise in their final draft of Before Sunset.
Julie Delpy's agent at the time tried to dissuade her from participating in this project both as a screenwriter and an actress, saying it was "a stupid movie no one is going to see," asking her to go to the gym instead. He fired her as a client the same day.
There are several references to James Joyce; Jesse and Celine meet at "Shakespeare and Co.", a bookstore named after the original Parisian bookstore and publishing house owned by Sylvia Beach, who was the first to publish Joyce's "Ulysses".
As Jesse and Celine are getting on the boat he says, "alright, alright, alright" which is Matthew McConaughey's famous catchphrase from 'Dazed and Confused' also written and directed by Richard Linklater.