Tidsrejsen (literally The Time Travel or The Voyage through Time in Danish) is a Danish television series in the form of a Nordic Christmas calendar that was shown over the Christmas period by the Danish Broadcasting Corporation in 2014. As per tradition for Nordic Christmas calendars, the series premiered on 1 December 2014 and its first season ran for 24 episodes. It was written by Poul Berg and directed by Kaspar Munk. Tidsrejsen was filmed mostly in the town of Dragør on Amager, south of Copenhagen. The series has science fiction elements, such as a time machine, and has themes of young love and general love, as well as family, the idea that actions have consequences and the idea that people decide their own fate in life.

The Danish Broadcasting Corporation described the Christmas calendar series as "Back to the Future meets the romantic comedy", and there are indeed many references to the popular film trilogy, among other time travel films.

The series was rewritten into a novel by the main writer Poul Berg, and was released the same year in 2014. It follows the script for the TV series faithfully but with some added details.

A second novel written by Merlin P. Mann, taking place between season 1 and 2 will be published in November 2024.

In 2023, the series was renewed for a second season, which was released in December 2024.

A Spin-off of the series is in the works, set to be released in 2025.