Question

What is the longest book in existence? (That is not informational, i.e. dictionary, textbook)

Answer 1

I would say the bible is the longest book in existence because it has been written in for thousands of years. From the time of Adam and Eve.

Hope this answered your question!

Answer 2

A la recherche du temps perdu by Marcel Proust contains an estimated 9,609,000 characters (each letter counts as one character. Spaces are also counted, as one character each). The title translates to "Remembrance of Things Past".