The original 'adult' novels are published monthly in two strands, the "Past Doctor" novels, which slot in between televised stories, and the Eight Doctor novels, which follows on from the end of the series. Virgin Books published the series from 1991 until 1996, when they launched a spin-off series starring Professor Bernice Summerfield, due to the license being taken back by the BBC, who have been publishing the series ever since.