Book excerpt: For over fifty years, the BBC's Doctor Who has taken viewers on adventures across time and space. At the same time, the programme has crossed genres and styles. From science fiction to action, horror to comedy and back again. Regeneration: The Changing Style of Doctor Who offers a penetrating looks at the way different showrunners, producers and script editors shaped the Time Lord's adventures. Analysing each era in sequence, it looks at story styles, the character of the Doctor and his intrepid companions, and the nature of the villains and monsters they faced, as well as the portrayal of the Time Lords. An essential guide both for new fans wanting a primer on the programme's history and for longstanding enthusiasts seeking a fresh perspective on eras they thought they knew.