The current doctor (the tenth) will regenerate in the final special of 2009. Other than that there have been loads (old age, exile by Time Lords, radiation from cave, falling off radio telescope, etc ....
Time Lords (the Doctor) can regenerate twelve times. But who knows, the Doctor might be so awesome he can regenerate more times.
He will regenerate into the 12th Doctor.
He'll regenerate into the 13th Doctor.
The fourth Doctor fell off a bridge.
Eventually yes, he will regenerate into the twelfth Doctor.
Romana was another Time Lord, like the Doctor.
In the movie, The End Of Time.
Time Lords regenerate because they have a injury or something is wrong, it's their way of healing themselves.
It is unknown, the Eighth Doctor only appeared in a movie.
He would regenerate.
We won't know how or why until he actually regenerates.
Trenzalore (his final resting place), in the town of Christmas
The 6th Doctor regenerated after suffering unspecified injuries when The Rani attacked the TARDIS causing it to crash.
Because it was time for him to go he didn't want to be the doctor anymore and that's why they regenerate so that they can go from actor to actor without it being obvious
NuWho -- Episode name : Utopua/The Sound of Drums/Last of the Time Lords. This is when we see Derek Jacobi regenerate into John Simm
I dont think he was in an ocean... He was in the Tardis...?
He was poisoned and used the last of the antidote to save his companion, Peri.
The girl in the end of Day of the Moon seems to be Amys daughter and she can regenerate since she was in the tardis.
The eighth Doctor regenerated offscreen and nothing is known about how or why he regenerated. The eighth Doctor appeared onscreen only once in a TV movie. We know th Time War happened between the TV movie and the start of the 2005 series. It's widely assumed that whatever the Doctor did to end the Time War caused him to regenerate.
Currently humans cannot regenerate at all
On June 1st, 2013 it was confirmed that Matt Smith will be leaving the show, his Doctor will regenerate in the Christmas special.
He regenerated because his current body was getting old, so it was of natural causes.
If the Doctor regenerates then the T.A.R.D.I.S regenerates. If the T.A.R.D.I.S blows up or something, then the Doctor will die. It basically has a part of him made in it.
The doctor can regenerate 12 times in total, so far he has regenerated 11 times and throughout those times 10 different actors have been played by the doctor. That doesn't mean the show will end when the regeneration limit is up, the Master gained a whole new cycle of regenerations so they will find away for the Doctor to go over the limit.