The TARDIS (; acronym for "Time And Relative Dimension(s) In Space") is a fictional hybrid of the time machine and spacecraft that appears in the British science fiction television series Doctor Who and its various spin-offs. Its exterior appearance mimics a police box, an obsolete type of telephone kiosk that was once commonly seen on streets in Britain. Paradoxically, its interior is shown as being much larger than its exterior, commonly described as being "bigger on the inside".

Due to the significance of Doctor Who in popular British culture, the shape of the police box is now more strongly associated with the TARDIS than its real-world inspiration. The name and design of the TARDIS is a registered trademark of the British Broadcasting Corporation (BBC), despite the fact that the design was originally created by the Metropolitan Police Service.