21 May (releases)


 * 1966 - "The O.K. Corral" was broadcast on BBC1, bringing to an end the regular practice of titling individual episodes until 2005.
 * 1966 - Part one of TV Comic story The Secret of Gemino was first published.
 * 1977 - Part two of TV Comic story Kling Dynasty was first published.
 * 1980 - Part six of Doctor Who Weekly comic story Doctor Who and the Dogs of Doom and part two of Yonder... The Yeti were first published.
 * 1981 - The Doctor Who Programme Guide was first published by Target Books.
 * 1987 - The Doctor Who Fun Book was first published by Target Books.
 * 2005 - The Empty Child was first broadcast on BBC One. Later, Special Effects aired on BBC Three.
 * 2009 - Doctor Who Adventures comic story Code Freeze was first published.
 * 2011 - The Rebel Flesh was first broadcast on BBC One. Later, Double Trouble aired on BBC Three.