Events that occurred on 20 September.
On Earth
- 1886 – Inkling Charles Williams is born.
- 1944 - J.R.R. Tolkien writes Letter 80b.
- 1947 – J.R.R. Tolkien writes Letter 110.
- 1948 – Author George R. R. Martin is born.
- 1962 – Cartoonist Bill Amend is born.
- 1963 – J.R.R. Tolkien writes Letter 247.
- 1982 – Mr. Bliss is published in the UK.
- 1986 – Oxonmoot 1986 at Oxford Town Hall.
- 1991 – Oxonmoot 1991 at University College.
- 1992 – The 1992 radio adaptation of Leaf by Niggle is aired on BBC Radio 5.
- 1996 – Oxonmoot 1996 at University College.
- 1997 – Oxonmoot 1997 at Exeter College.
- 2003 – Oxonmoot 2003 at St Hugh's College.
- 2013 – Oxonmoot 2013 at Lady Margaret Hall.
- 2018 - Oxonmoot 2018 at St Antony's College.
- 2020 - Oxonmoot 2020 held online due to the Covid-19 pandemic.
In Arda
- T.A. 3018:
- Gandalf gains entrance to Edoras and warns them about Saruman. Théoden tells him 'Take any horse, only be gone ere tomorrow is old!'.
- Two covered carts leave Bag End for Frodo's new house in Crickhollow. They convey the furniture and goods that Frodo has not sold by way of the Brandywine Bridge.
- Boromir travels towards Rivendell to ask for counsel.