Events that occurred on 31 May.
 On Earth
- 1912 - German translator Margaret Carroux is born.
- 1944 - J.R.R. Tolkien writes Letter 72.
- 1981 - The thirteenth episode of the 1981 radio adaptation of The Lord of the Rings is aired on BBC Radio 4.
 In Arda
Note: Months of the Shire Calendar only have 30 days, so no events have nor will happen on the 31st.