According to Doctor Who history, the TARDIS (Time and Relative Dimension in Space), is the Doctor's means of transport from A to B through time, as well as his home. All Gallifreyan Time Lords had a TARDIS as a means of transport, which could take any form, however the chamelon circuit on the TARDIS jammed in 1963 and so it remained as a Police Box.
The design for the Doctor's TARDIS is based on the now-defunct Police Boxes which were a common sight on streets in the UK prior to the advent of two-way radios - they contained emergency telephones for use by both the public and the police. The idea to use the Police Box design was originally conceived by Anthony Coburn, author of the first episode The Unearthly Child; it is believed that this particular model was built by Ron Oates of the BBC's visual effects department.
The overall appearance of the TARDIS has changed little since the first episode in 1963. Research reveals that this model first appeared in the second season in The Romans, 1965, where it can be seen falling over a cliff. It could have been made as early as 1963 when several models of differing scales were all constructed. It can clearly be seen in the still illustrated above from The Dalek's Masterplan, Season 3, 1965-1966. According to Anthony Sibley, who has researched the models in-depth, this version is easily recognisable as it is the only model to have the wider door rail at the bottom, all others have even width door rails. One of its last screen appearances as a set-used model is in the first appearance of John Pertwee as the third Doctor, as seen in the still illustrated above from Spearhead From Space, 1970. It was then photographed for use in the title sequences for the fourth Doctor, Tom Baker, 1974-1979, where Bernard Lodge, of the BBC's graphic design department, employed the famous Slit Scan technique, the same technique used by Stanley Kubrick for the Star Gate sequence in 2001: A Space Odyssey released in 1968. This model was then retired, and given to the current owner, Joanna Ball, who was Bernard Lodge's assistant. From the late 1970s to circa 2003, the image of this model has been used on various pieces of merchandise including the 1979 soundtrack, calendars, t-shirts and posters.
Over the years since its first appearance, the TARDIS has entered the nation's consciousness, and the word is now synonymous with something deceptively large on the inside. It has even inspired artists - in the summer of 2001, the contemporary artist Mark Wallinger created an installation entitled Time And Relative Dimensions In Space using two full-scale replicas of the TARDIS, designed by Anthony Sibley, outside the Museum of Natural History in Oxford.