A TARDIS Instruction Manual, also known as a TARDIS Manual or TARDIS Handbook, was a book that instructed in the piloting and workings of a TARDIS.
The Doctor's manual
The Fourth Doctor owned a handbook specific to the Type 40 model. While making modifications to the TARDIS, he read aloud the passage "when making modifications, it's extremely important to shut everything down, except that which is not necessary to shut down", and commented that he found it quite sensible. (TV: The Horns of Nimon) On other occasions, the Doctor disagreed strongly with the manual, at one point even tearing out one of its pages. (TV: The Pirate Planet) On one occasion, he told Romana that having the TARDIS manual quoted to him was bad for his concentration. (AUDIO: The Sands of Life)
Tegan Jovanka tried to understand the manual when she accidentally set the TARDIS in flight while trying to get herself off of the Monarch's ship. She called it gibberish, finally throwing it to the floor and stamping on it. (TV: Four to Doomsday)
Peri Brown found a TARDIS handbook propping open a vent in the Sixth Doctor's workshop; he admitted he'd started reading it once. On Peri's urging, he used it to figure their way out of a power failure. (TV: Vengeance on Varos)
When an alien creature tried to get into the TARDIS, the Seventh Doctor consulted the manual for help. However, the creature had already breached the ship's dimensional interfaces, which included time, and so the manual was already destroyed even though the creature had not yet broken into the ship. (PROSE: Cat's Cradle: Time's Crucible)
The Eighth Doctor once went looking for the TARDIS manual in the library, but became distracted by the other books there. (AUDIO: Storm Warning) He had a quick-start guide, while the manual itself had its own street in the TARDIS. (AUDIO: Orbis) Sarah Jane Smith once happened upon a room in the Eighth Doctor's TARDIS in which several thousand volumes of the TARDIS Instruction Manual were kept; she took this to mean the single book she had seen the Fourth Doctor use was just the introductory volume. (PROSE: Interference - Book Two)
Fey Truscott-Sade once used the Eighth Doctor's manual to pilot the TARDIS to Gallifrey, (COMIC: The Final Chapter) although the Doctor later revealed that the Threshold had secretly guided her actions by giving her an implant that allowed her to read the manual, which was printed in Gallifreyan. (COMIC: Wormwood)