1. Classified by content and subject.
novel
biography
history
science
art
politics
economy
philosophy
religion
natural science
2. Classification according to form and structure
essay
poetic sentiment
drama
thesis
diary
3. According to the classification of readers
readings for children
juvenilia
Adult reading materials
Academic monograph
4. Classification by publication form
Paper books
ebook / electronic book / e-book
Audio books
The above classification methods are only common and not comprehensive. In fact, there are many other classification methods, such as classification by language, country and era.