Rengeration is the process by which a Time Lord saves themselves from dying by transforming into another form. When a Time Lord successfully completes a regeneration they are like a new person, as they have a new body, new voice, and a new personality. The only thing that stays is the memories of the time lord. In the revived series of Doctor Who the regeneration process has the Time Lord stand upright with their hands pointing towards the ground, and the energy flowing conceals the head and hands. This style of regeneration has been seen three within the series, once was The Parting of the Ways where the Ninth Doctor had to regenerate after saving Rose Tyler by absorbing the Time Vortex, and again when The Master went through the same process, to transform from Professor Yana into Mr. Saxon. The Tenth Doctor begins a regeneration process in The Stolen Earth, but does not complete it, instead he transfers the regeneration energy into his hand.
A Time Lord is said to have a limited number of Regenerations, so the Tenth doctors failed regeneration would have counted as the 11th incarnation, meaning The Doctor only has two more regenerations left. The Eleventh Doctor would be the twelfth regeneration, but the eleventh body.
 Regeneration Time Line
- First Doctor - Regenerated in Series 4 of the original series, the cause was old age.
- Second Doctor - Regnerated in Series 6 of the original series, the Time Lords forced him to regenerate.
- Third Doctor - Regenerated in Series 11 of the original series, the cause was giving his life to destroy an enemy.
- Fourth Doctor - Regenerated in Series 18 of the original series, the cause was defeating the Master.
- Fifth Doctor - Regenerated in Series 21 of the original series, the cause giving up an antidote to save Peri Brown.
- Sixth Doctor - Regnerated in Series 24 of the original series, the cause was unknown motives.
- Seventh Doctor - Regenerated in the TV Movie for the original series, the cause was being shot by a gang member on Earth 1999.
- Eighth Doctor - Regneration is somewhere between the Movie, and the revived series, with an unknown cause.
- Ninth Doctor - Regnerated in series 1 of the revived series, the cause was absorbing the Time Vortex.
- Tenth Doctor - Regenerated in Series 4 of the revived series, the cause was being shot by a Dalek, this regeneration's power was transferred to the doctors hand.
- Eleventh Doctor - Was obliterated whilst saving Wilfred Mott. However the regeneration did not take place immediatly; during the time he had left, he revisited all his past companions and said his farewells. When he did finally regenerate, it was with such force that it destroyed parts of the TARDIS, causing it to set alight.