Laws of Time

The Laws of Time regulated Time Lords' use of their power to travel in time. Beyond the First Law, however, the exact details of these laws were not well understood, nor were the punishments for breaking the laws particularly clear.

Meeting out of Order
Rassilon's First Law of Time stated it was forbidden, and thus generally impossible, for Time Lords to meet each other out of temporal sequence, (PROSE: Goth Opera) and specifically prohibited a Time Lord from meeting their former selves. (TV: The Three Doctors) Despite this, the Doctor on numerous occasions did just that — either accidentally (TV: Time Crash) or through Time Lord sanction. (TV: The Three Doctors, The Five Doctors) Charlotte Pollard broke the First Law of Time by travelling with the Doctor's sixth incarnation after having been the companion of his eighth self, thus exposing the Doctor to his own future. (AUDIO: Brotherhood of the Daleks) Similarly, the Seventh Doctor may be said to have broken the First Law of Time by leaving messages for himself. (PROSE: No Future) The law had a moral basis as well as a legal one. (PROSE: Love and War)

Influencing History
The Seventh Doctor stated that interfering in Gallifrey's past time travel experiments was against the First Law. (PROSE: Cat's Cradle: Time's Crucible) Whether or not it was First, there was a Law traditionally preventing Gallifrey's 'present' from interacting with its own subjective past or future. (PROSE: Lungbarrow)
 * Depending on the interpretation, the Doctor may have been speaking about interfering in any planet's past which would affect their development.

The Fourth Doctor refused to bring back the Kastrian Eldrad (regenerated after a gap of about 150 million years) to its native time because that would have "contravened the First Law of Time", a "distortion of history". (TV: The Hand of Fear)

The Ninth Doctor once told Rose Tyler that "there used to be laws preventing this sort of thing" in reference to her interference with her own past. However, he failed to enumerate them. (TV: Father's Day) Likewise, the Brigadier's encounter with his past self was described by the Doctor's fifth self as being bad, but not as a specific violation of the First Law. (TV: Mawdryn Undead)
 * It was therefore possible that other laws of time were concerned with the Blinovitch Limitation Effect, the more generalised problem of any being meeting a past version of themselves. 

During his ninth and tenth incarnations, the Doctor willingly caused tiny loops in the timeline of those specific incarnations, without citing a violation of the First Law. Indeed, the Doctor once told Martha Jones that "crossing into established events is strictly forbidden, except for cheap tricks". (TV: Father's Day, Smith and Jones)

Avoiding Voids
Upon entering a slow time conversion unit, the Seventh Doctor stated that the first law of space-time travel was "avoid voids" (PROSE: The Highest Science) referring to the White and Black Voids outside of time and space, (TV: The Mind Robber, Logopolis) the Gateway between N-Space and E-Space, (TV: Warrior's Gate) and the Void between all universes. (TV: Army of Ghosts/Doomsday)

Other Laws of Time
Another of the Laws of Time stated that an object from a non-existent timeline cannot be present in the current timeline. Cousin Justine of the Faction Paradox, a time-aware faction opposed to the Time Lords, which, as their name indicated cultivated and revelled in time paradoxes, had a mask from another timeline. (PROSE: Alien Bodies)

In his eight incarnation the Doctor said that learning "anything about future Gallifreyan history" would seriously unbalance the concept of causality. When he proceeded to nevertheless break this law, he claimed, "I'm breaking one of the major Laws of Time...It could be the third." (PROSE: Alien Bodies)

Other information
Before the Laws were actually enforced, a Time Lord librarian visited the histories of planets. (PROSE: Love and War)

The Fifth Doctor stated that Time Lords served Time, rather than the other way around. (AUDIO: The Axis of Insanity) They were pledged to uphold the Laws of Time and to prevent alien aggression, as the Fourth Doctor specified: "only when such aggression is deemed to threaten the indigenous population. I think that's how it goes." (TV: The Hand of Fear)

The Doctor stated that he was "...Defender of the Laws of Time" in his seventh and eighth incarnations. (TV: Remembrance of the Daleks, PROSE: Vampire Science)

The Laws of Time became weakened during the Second War in Heaven so that future events filtered back to interact with events prior to the war's outbreak. (PROSE: Alien Bodies, The Taking of Planet 5)

The Tenth Doctor said he was in control of the Laws of Time after the destruction of the Time Lords in the Last Great Time War. (TV: The Waters of Mars)

The Eleventh Doctor said that the Laws of Time were too powerful for anyone to totally control, and that repeatedly acting in disregard of them would make time "fold in on itself", threatening to destroy all of existence. (GAME: City of the Daleks)

After the destruction of time, caused by the TARDIS exploding, it was implied by the Eleventh Doctor that the laws of time no longer applied and therefore used the situation to meet himself and buy more time. (TV: The Big Bang)

Leis do Tempo