Who Goes Gold
Excluding the Children in Need specials, this is the 50th episode of Doctor Who since the series returned in 2005. Hasn't time flown?
The Big Read
The current holder of the record for being the World's Largest Library is the Library of Congress in America, which holds approximately 29 million books.
Steve Pemberton becomes the second member of The League of Gentlemen to guest star in Doctor Who. Last year Mark Gatiss (who has also written for Doctor Who) guest starred in The Lazarus Experiment.
Steve previously co-starred alongside David Tennant in an episode of the revival of Randall And Hopkirk (Deceased).
The (Other) Two Doctors
Alex Kingston is perhaps best know for playing Dr. Elizabeth Corday in 158 episodes of US medical drama ER.
The Write Stuff
Writer Steven Moffat, who is to take over as Doctor Who's Show Runner and Head Writer, has won both Hugo and Bafta Awards for his previous Doctor Who scripts. Steven is the only writer other than Russell T Davies to have contributed scripts to all four series of the revived show.
The main library scenes for the episode were filmed at Swansea Library and Brangwyn Hall, Swansea.
Weapon Of Choice
The 'squareness gun' used by River Song is similar in function to the one used by Captain Jack in The Doctor Dances.
The cartoon that can be seen on the girl's TV is Pedro & Frankensheep.