Events that occurred on 12 September.
On Earth
- 1915 - J.R.R. Tolkien writes "A Song of Aryador".
- 1931 - Actor Ian Holm is born.
- 1951 - Third day of the Congrès Internationale de Philologie Moderne at the University of Liège, a conference in which J.R.R. Tolkien delivers the paper "Middle English 'Losenger'".
- 1960 - J.R.R. Tolkien writes Letter 224.
- 1965 - J.R.R. Tolkien writes letters 276 and 277.
- 1966 - J.R.R. Tolkien writes a letter to Rose MacNamara.
- 1981 - Author and librarian William Ready dies.
- 2010 - Bulgarian Tolkien Society's 6th Tolkien-Fest in Sofia.
- 2012 - An updated edition of Charles Dixon and David T. Wenzel's The Hobbit is published.
- 2013 - The Hobbit, illustrated by Jemima Catlin, is published.
- 2013 - Tolkien Calendar 2014 is published.
- 2014 - Oxonmoot 2014 at Lady Margaret Hall.
- 2014 - Tolkien at Exeter College: How an Oxford undergraduate created Middle-earth by John Garth is published.
- 2015 - Oxonmoot 2015 at St Antony's College.
- 2025 - Actor Sean Astin elected President of the Screen Actors Guild–American Federation of Television and Radio Artists (SAG-AFTRA).