Events that occurred on 18 December.
 On Earth
- 1944 - J.R.R. Tolkien writes Letter 92.
- 1949 - J.R.R. Tolkien writes Letter 122.
- 1955 - The sixth and final episode of 1955 radio series of The Fellowship of the Ring airs on the BBC Third Programme.
- 1963 - J.R.R. Tolkien writes a letter to Jonathan Hepworth.
- 1965 - J.R.R. Tolkien writes Letter 282.
- 1977 - Actor Cyril Ritchard dies.
- 2002 – The Lord of the Rings: The Two Towers premières.
- 2007 - MGM and New Line Cinema announce the The Hobbit (film series).
 In Arda