A lie or lying was the action of telling something that was not the truth.
While in London, the Ninth Doctor lied to Rose Tyler that he was leaving her flat to get some privacy and was not going to wander off only to then investigate the Slitheen crash. (TV: Aliens of London) He also lied to Jack Harkness that his sonic screwdriver could not open a door in order to trick Jack into revealing he possessed a Sonic blaster. (TV: The Doctor Dances) One Dalek accused the Doctor of lying when he declared he personally killed the Dalek race during the Last Great Time War. (TV: Dalek) The Doctor himself accused the Editor on Satellite Five of lying to the people within the Fourth Great and Bountiful Human Empire. (TV: The Long Game)
The Tenth Doctor occasionally lied. (TV: School Reunion, The Fires of Pompeii) He believed he did it to make himself feel better. (TV: Gridlock) Although, he occasionally lied for strategic purposes, such as tricking the Family of Blood that he was still in human in order to tamper with their ship's equipment. (TV: The Family of Blood) He could also deduce when others were lying, such as Novice Hame's lie that the Sisters of Plenitude were not harming patients on New Earth (TV: New Earth) and that Sarah Jane Smith was actually researching Krillitane activity rather than writing a journal article about the local high school's improving exam results as she claimed. The Doctor himself likewise initially lied to her that he was a human Physics teacher at the school called John Smith. (TV: School Reunion) He also claimed "John Smith" was his real name to a group of tourists when it actually wasn't, a lie the group saw through. (TV: Midnight)
The Eleventh Doctor made a habit of lying, both to companions (TV: Flesh and Stone, The Lodger, The Impossible Astronaut, The Almost People, Let's Kill Hitler, The Wedding of River Song, The Name of the Doctor) and enemies, (TV: Victory of the Daleks, The Doctor's Wife, The Snowmen, Journey to the Centre of the TARDIS, Nightmare in Silver) so much so that Amy Pond could sometimes tell when he was lying. (TV: The Doctor's Wife, Asylum of the Daleks) This led River Song to declare "Rule One: The Doctor lies." (TV: The Big Bang, The Wedding of River Song) The Eleventh Doctor even lied about his age, so much so that was unsure he was even lying about it when speaking to the War Doctor. (TV: The Day of the Doctor) Given his history, the Time Lords constructed a Truth Field on Trenzalore to force the Doctor to speak truthfully. (TV: The Time of the Doctor)
The Twelfth Doctor also lied. He lied to Clara Oswald, putting her in a dream scenario to test how far she would go to convince him to save Danny Pink. (TV: Dark Water) He later lied to Bill Potts that was assisting the monks in order to test if she was under their control. (TV: The Lie of the Land) Ohila confessed to the Doctor that she always assumed he was lying because "it save[d] time." (WC: Prologue) Clara noted however that the Doctor lied with purpose, trying to give those in danger hope so they would run from danger faster. (TV: Flatline)
When he met the Dalek Prime Strategist, the Tenth Doctor came to believe that its claim of being proud of using a ruined Dalek War Machine was a lie, sympathising with lying as a coping mechanism. (COMIC: Defender of the Daleks)
In her time with the Doctor, Clara Oswald became adept at lying something that, along with her lack of concern in doing it, gave the Doctor concern. (TV: Flatline) She later boasted of being "an incredible liar", something that Danny Pink mournfully agreed with. (TV: Death in Heaven)