The creative team were initially worried about casting the 22-year-old Carey Mulligan in the role of a 16-year-old, but were convinced by her screen test. Rosamund Pike reportedly really wanted the small part of Helen, because "no one ever lets me be funny".
Carey Mulligan mentioned in an interview at the Sundance Film Festival that some of the most enjoyable moments of filming were when there were actors who only came in for a day or so, like Sally Hawkins and Emma Thompson, and she particularly enjoyed the four scenes she shot with the latter, whom she described as being "amazing", and called her acting "brilliant".
Director Lone Scherfig says she experimented with giving the actors options during scenes. For instance, she told Peter Sarsgaard that if he felt like it he could start a conversation with an extra playing a doorman in one scene despite there not being any written dialogue.
The author of the original account, Lynn Barber stipulated in her contract that she would be allowed to see and comment (but not alter) every draft written by the screenwriter, Nick Hornby. She mentioned that she was happy with most of the changes, but her one regret was that Hornby changed the name of her lover, Simon, to David, which was her real husband's name. She stated that "I wish in retrospect I'd put up a fight".
In the beginning of the film, Jenny's fringe is neatly parted. As she becomes more and more involved with David, her fringe starts to descend until it is completely down. This shows she is now a part of his world. Then, as she starts to move away from him, her hair becomes parted again.
Whilst the screenplay was being written, the producers were looking for directors; Beeban Kidron was on board for a year and half, and helped develop the script. She was forced to pull out because of a commitment to Hippi Hippie Shake.