Here are the categories for the 2018 Back to the Classics Challenge (and my tentative list):
1. A 19th century classic - any book published between 1800 and 1899.
The Wrong Box by Robert Louis Stevenson & Lloyd Osbourne  (4/3/18)
2. A 20th century classic - any book published between 1900 and 1968. Just like last year, all books MUST have been published at least 50 years ago to qualify. The only exception is books written at least 50 years ago, but published later, such as posthumous publications.
Go Down, Moses by William Faulkner  (3/30/18)
3. A classic by a woman author.
Enter a Murderer by Ngaio Marsh [Golden Age Mystery; 1935] (2/7/18)
4. A classic in translation. Any book originally written published in a language other than your native language. Feel free to read the book in your language or the original language. (You can also read books in translation for any of the other categories). Modern translations are acceptable as long as the original work fits the guidelines for publications as explained in the challenge rules.
The Song of Roland by Anonymous; Trans by Dorothy L. Sayers (oldest manuscript circa 12th C)
5. A children's classic. Indulge your inner child and read that classic that you somehow missed years ago. Short stories are fine, but it must be a complete volume. Picture books don't count!
The Adventures of Paddy the Beaver by Thornton W. Burgess  (2/8/18)
6. A classic crime story, fiction or non-fiction. This can be a true crime story, mystery, detective novel, spy novel, etc., as long as a crime is an integral part of the story and it was published at least 50 years ago. Examples include The 39 Steps, Strangers on a Train, In Cold Blood, The Murder of Roger Ackroyd, etc. The Haycraft-Queen Cornerstones list is an excellent source for suggestions.
Death in Ecstasy by Ngaio Marsh (1936)
7. A classic travel or journey narrative, fiction or non-fiction. A journey should be a major plot point, i.e., The Hobbit, Unbeaten Tracks in Japan, Kon-Tiki, Travels with Charley, etc.
Life on the Mississippi by Mark Twain (1883) [3/10/18]
8. A classic with a single-word title. No articles please! Proper names are fine -- Emma, Germinal, Middlemarch, Kidnapped, etc.).
She by H. Rider Haggard (1886)
9. A classic with a color in the title. The Woman in White; Anne of Green Gables; The Red and the Black, and so on.
The Black Arrow by Robert Louis Stevenson (1888)
10. A classic by an author that's new to you. Choose an author you've never read before.
The Works of Charles & Mary Lamb II by Charles & Mary Lamb (1833)
11. A classic that scares you. Is there a classic you've been putting off forever? A really long book which intimidates you because of its sheer length? Now's the time to read it, and hopefully you'll be pleasantly surprised!
Melmoth the Wanderer by Charles Robert Maturin (1820)
12. Re-read a favorite classic. Like me, you probably have a lot of favorites -- choose one and read it again, then tell us why you love it so much.
The Count of Monte Cristo by Alexander Dumas [père] (1844)