The casting of Dave Chappelle as Kevin, Joe's (Tom Hanks) friend and confidant, came about because four years previously Chapelle was offered the role of Bubba in Forrest Gump (1994), Hanks' big blockbuster, which became a worldwide phenomenon. Chapelle turned down the role of Bubba because he felt Forrest Gump would flop at the box office. However when it became a huge success worldwide, and dominated the 1994 Oscars, Chapelle said he deeply regretted turning down the role of Bubba. Hanks, realizing this, promised to work with Chapelle on a future film as a result, and he suggested to director Nora Ephron he play the role of Kevin. Ephron agreed, and Chapelle eagerly accepted the offer to work with Hanks.
The scene where Joe accidentally closes the door of Kathleen's shop on the balloons was unscripted. Tom Hanks actually did that, and ad libbed the line, "Good thing it wasn't the fish." Nora Ephron thought it was so funny that she kept it in.
The children's bookstore scenes were filmed at Maya Schaper's Cheese and Antique Shop at 106 West 69th Street. The film makers wanted to use the antique shop because it had the quaint, homey feel they were going for. They sent the owner of the antique shop on vacation for a few weeks and while she was gone they turned the store into a children's bookshop. After filming was finished, they put everything back the way they had found it.
All of Joe and Kathleen's e-mails were put on the movie's official website, which Warner Bros. kept active until 10 May 2018.
Nora Ephron arranged for Meg Ryan and Heather Burns to work in a real New York City bookstore in preparation of their roles prior to filming. The store was Books of Wonder in Manhattan, and the jobs lasted for about a week.