Time And Relative Dimension In Space. Described by the Doctor as the sports car of time travel, it is bigger in the inside and is capable of many amazing feats. The Doctor's TARDIS is a Type 40 TARDIS, which he stole from a museum when he was young.
The Doctor's TARDIS is stuck in the form of a Police Box due to a faulty chameleon circuit. Police Boxes had a telephone inside to call for help and could also be used by constables to hold a suspect until back up arrived. The Doctor is quite fond of his blue box and has stated so on a few occasions. Aside from the Doctor himself and other Time Lords, the only other person capable of flying it is River Song, a companion of the Doctor. The Doctor also gave Rose Tyler and Donna Noble lessons in how to fly it.
Some TARDIS features:
When the Doctor traveled to a bubble universe, he was trapped by an entity known as 'House' who ate TARDISes. House extracted the soul of the Doctors TARDIS and placed it in the body of a human woman for a short period of time. She demonstrated knowledge of future events, and indicated that she did not experience time in a linear fashion. While in human form she asked that the Doctor call refer to her as 'Sexy' as he normally does while they are alone. She referred to the Doctor as her thief, but also stated that she wanted to get out to see the universe and so she stole a Time Lord. When the Doctor told her that she was not very reliable, and she did not always taken him when her wanted to go, she responded with "No, but I always took you where you needed to go". Once her soul had being returned to the TARDIS, she lost the ability to communicate with the Doctor.