Russell T. Davies wrote this episode because Billie Piper requested that she would be given a comic role in the new season, as a counterpoint to the often very serious material she had tackled the year before.
In the beginning, Billie Piper didn't know that she would be squirted with water in the lift. Russell T. Davies kept it in the final cut as he thought it was too funny to cut it. David Tennant wanted to watch this happen for the first time.
The Converse Chuck Taylor All Star trainers that the Tenth Doctor wears are actually David Tennant's personal shoes.
Adjoa Andoh who played Sister Jatt would later turn up in a semi-regular role as Martha Jones' mother Francine in Season Three.
The giant "BAD WOLF" graffiti written on a paved public area of Rose's estate (seen in The Parting of the Ways (2005)) is still visible, though faded, at the start of the episode.