The TARDIS (Time And Relative Dimension In Space) is the Doctor's time machine. It can travel to any point in time and space, but the Doctor can never fully control it. The Doctor explains that TARDISes are not built, but they are grown like plants. The TARDIS is alive and has a mind of its own. In the episode "The Doctor's Wife" when the Doctor is able to communicate directly with its mind, the TARDIS explains that it did not always take him where he wanted to go but that "I always took you where you needed to go."