John Smith gives the names of his parents as Sydney and Verity. This is a reference to Sydney Newman (creator of "Doctor Who" (1963)) and Verity Lambert (the show's first producer).
In John Smith's book, "A Journal of Impossible Things", sketches of previous actors who have played the Doctor are shown, marking the first time that the 2005 series has explicitly depicted the Doctors from "Doctor Who" (1963) and Doctor Who (1996) (TV). The actors depicted on screen were William Hartnell, Peter Davison, Colin Baker, Sylvester McCoy and Paul McGann. Images of the Journal that were published on the BBC website reveal that the other remaining Doctors, Tom Baker, Jon Pertwee, Patrick Troughton, Christopher Eccleston, and David Tennant himself, were also illustrated on the page.
Rose Tyler mention: Rose appears in John Smith's 'A Journal of Impossible Things'.
The fob watch that figures so prominently in this episode (and through the rest of the third series) was originally seen in the early series one episodes as a knob on the TARDIS control console. It is clearly seen in closeups of Christopher Eccleston's hands as he sets the controls in "Doctor Who: The End of the World (#1.2)" (2005).
This episode and part two "The Family of Blood" were adapted by scriptwriter Cornell from his 1995 Doctor Who novel, "Human Nature". This marks the first time in Doctor Who history that a novel based upon the series was adapted as an episode. Many changes were made in transferring the novel to the screen. The original book featured the Seventh Doctor and his companion, Benny Sommerfield, and the Doctor's motive for becoming human was to study the human condition, not to flee aliens.