The Notion Club Papers is the title of an abandoned novel by J. R. R. Tolkien, written during 1945 and published posthumously in Sauron Defeated, the 9th volume of The History of Middle-earth. It is a space/time/dream travel story, written at the same time as The Lord of the Rings was being developed. The story itself revolves around the meetings of an Oxford arts discussion group called the Notion Club, a fictionalization of (and a play on words on the name of) Tolkien's own such club, The Inklings.

During these meetings, Alwin Arundel Lowdham discusses his lucid dreams about Númenor; through these dreams, he "discovers" much about the Númenor story and the languages of Middle-earth (notably Quenya, Sindarin, and Adûnaic — the last very interesting since it is the sole source of most of the material on this language). While not finished, at the end of the given story it becomes clear Lowdham himself is a reincarnation of sorts of Elendil. (Alwin is a modernization of the name Ælfwine, Old English for Elf-friend, or Elendil in Quenya.) Other members of the Club also mention their vivid dreams of other times and places.

Tolkien not only created fictional meetings for these papers; he also created a fictional history for the manuscript of the papers. According to the papers, the meetings occurred in the 1980s; they even mention events that occurred in the 1970s and 1980s. About one-quarter of the papers were found among sacks of waste paper in 2002 at Oxford by a Mr. Green. Mr. Green published a first edition containing excerpts from these papers, indicating that they were written during the 1980s by one of the participants. Two scholars read the first edition, asked to examine the manuscripts, and then submitted a full report. The "Notes to the Second Edition" mentions the contradictory evidence in dating the manuscripts, and an alternative date is presented: they may have been written in the 1940s.

These papers, which make a number of comments on Lewis' Space Trilogy, remind one of C. S. Lewis' commentary to Tolkien's poem The Lay of Leithian, in which Lewis created a fictional history of scholarship of the poem and even referred to other manuscript tradition to recommend changes to the poem.

The Notion Club Papers may be seen as an attempt to re-write The Lost Road, published and discussed in The Lost Road and Other Writings, as being another attempt to tie the Númenórean legend in with a more modern tale. There is, however, no direct connection between the modern settings of the two stories within the fictional frame.

According to C.J.R. Tolkien, had his father continued The Notion Club Papers, he would have linked the real world of Alwin Lowdham with his eponymous ancestor Ælfwine of England (who compiled the Lost Tales) and with Atlantis. One of the members of the Notion Club, one Michael George Ramer, combines lucid dreams with time-travel and experiences the tsunami that sank Númenor. He can't tell if its history, or fantasy, or something in between.

The Notion Club Papers mentions a great storm occurring during 1987 in England, and indeed the fictional commentary, placing the 'actual' storm on 12 June, notes that this provides evidence that it could not have been written in the 1940s unless one was prepared to concede that "some person or persons in the nineteen-forties possessed a power of 'prevision'". In real life the Great Storm of 1987 occurred in October of that year.