Events that occurred on 12 May
 On Earth
- 1917 - J.R.R. Tolkien is declared fit for home service.
- 1879 - Percy Bates is born.
- 1944 - J.R.R. Tolkien writes Letter 68.
- 1955 - J.R.R. Tolkien writes a letter to Rayner Unwin.
- 1965 - J.R.R. Tolkien writes Letter 269.
- 2004 - "Reflections", the ninth set in The Lord of the Rings Trading Card Game is released.
 In Arda
- There are no known events for this day.