On 21 May, a number of things set in or relevant to the Doctor Who universe were released or published.
- 1966 - "The O.K. Corral" was broadcast on BBC1.
- 1966 - Part one of the TV Comic story The Secret of Gemino was first published.
- 1977 - Part two of the TV Comic story Kling Dynasty was first published.
- 1981 - The Doctor Who Programme Guide was first published by Target Books.
- 1987 - The Doctor Who Fun Book and the novelisation of The Faceless Ones was first published by Target Books.
- 2005 - The Empty Child was first broadcast on BBC One. Later, Special Effects aired on BBC Three.
- 2009 - The 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.
- 2015 - Suburban Hell was first released by Big Finish.
- 2015 - The novelisation of City of Death was published by BBC Books and released as an audiobook by BBC Physical Audio.