One Day is a novel by David Nicholls, published in 2009. A couple spend the night together on 15 July 1988, knowing they must go their separate ways the next day. The novel then visits their lives on 15 July every year for the next 20 years. The novel attracted generally positive reviews and was named 2010 Galaxy Book of the Year. Nicholls adapted his book into a screenplay; the feature film, was released in August 2011, and a television series for Netflix, premiered on 8 February 2024.

Lone Scherfig is a Danish film director and screenwriter. She has been involved with the Dogme 95 film movement. Scherfig's movies are generally romantic comedies, including her film One Day (2011), based on the David Nicholls's novel of the same name.