At the San Francisco International Film Festival on Wednesday, writer-director Richard Linklater and actress-writer Julie Delpy took the stage at the Sundance Kabuki to discuss their film “Before Sunrise” and its sequel “Before Sunset.” In the first film, Jesse (Ethan Hawke) and Celine (Delpy) meet on a train in Europe; she’s going home to Paris, while he’s going to Vienna to catch a flight back to the United States. He convinces her to get off the train in Vienna with him and spend the night walking around the city and talking. Nine years later, they meet again in Paris in “Sunset,” now in their 30s and in relationships, to discover what might have been.

The third film, “Before Midnight,” which had its premiere Thursday as the festival’s closing night film, was made and takes place nine years after “Before Sunset”; the characters are now in their 40s, in a relationship together and have children. Screenwriter Michael Jones joined them as their interviewer, with an excellent set of prepared questions about their process for working on the films. He selected and showed a series of clips from the first two films, throughout the evening, to help frame the discussion.

Although Linklater wrote the screenplay for “Before Sunrise” with Kim Krizan and brought the actors in afterward, Delpy, Hawke and Linklater co-wrote “Before Sunset” and “Before Midnight” in what was a very collaborative process, in which they thought everything through–the motivations for why each character says and does everything–and had to agree on everything. When one person brings an idea to the group, Linklater explained, “You’re going to have two people going, ‘Hmm, let’s talk about that. What would that mean?’ And you might have two weeks of conversation and see if that would end up in a movie, and it’s going to be fully thought out.”

Delpy elaborated, “We really work together on every character. Sometimes, I will call Ethan on something he wrote about his character that I don’t think is right because it brings something that I think is wrong for Celine, or she wouldn’t have stayed if he was like that.”

Delpy articulated the difference between Jesse and Celine and how meeting up again in “Before Sunset” affected the latter.

“She’s pissed off that she’s in love with him in a way,” Delpy said. “She keeps resisting it. She is the less romantic one in a way, the more rational one. You know, she works in a job that’s rational. She’s not a creative person; she’s not a writer like he is. He can romanticize things. And I think she keeps shutting down that part of her, and then it’s all revived by seeing him again and him basically telling her that he loves her and that he’s loved her for years.”

Linklater talked about what it was like to have such a long “gestation period” between the films and how that lets them really explore the characters in depth.

“We’ve lived 19 more years since we started this,” he said. “We have eight kids between the three of us. All that is fodder. So much of our time together is spent talking about how things go in our own lives…In the movie, they’re on holiday but we had an idea for a long time for it to just be a regular Tuesday in their lives showing where they live and what that’s like, and that introduced a lot of domestic thinking about the characters.”

Delpy added, “We thought about where they are professionally, their friends, how they felt, what happened when they had a kid. We’re all using our life experience. Celine, how she felt when she had a kid. Maybe she didn’t say everything to Jesse.”

Linklater also pointed out that the process helps them “work through all the clichés.”

“Because there are a lot of things where, okay, you can’t do that because then that makes them unlikable characters who have some unattractive qualities,” she said. “But maybe we have an audience for these movies [who are willing to accept that] or we want to express something that we find honest in our own lives, that you don’t always see, that isn’t always attractive.”

“Before Sunrise” and “Before Sunset” are available at Green Library. “Before Midnight” opens in San Francisco on May 24.