While the length of any book varies with language as well as format, this list contains many of the longest novels ever published. Although I have included all that I could find, it is biased toward works published in English as that made them much easier for me to identify.
I have endeavored to include only novels, works intended as fiction, and not religion or mythology. Each is a single work, that is, work thought of as one novel by the author even if published in multiple volumes for convenience. If part of a series, only the first book was considered for inclusion in this list. English editions are listed where existent, but many of the longest works have yet to be translated.
According to Wikipedia, "Nansō Satomi Hakkenden" is currently the longest novel in the world.