When reading, readers can find that each book has a theme, which is the core idea or theme to be expressed in this book. The theme of bibliography refers to the theme or subject field enjoyed by a series of books. For example, documentary literature, historical novels and science fiction are the themes of the bibliography.

Bibliographic theme is an important basis for readers to choose books. If a reader likes books on historical themes, he can choose his favorite books from the bibliography of historical novels. At the same time, bibliography also provides readers with more choices, which can make them better understand books on specific topics or fields.

The theme of the bibliography also helps publishers to conduct market research and book sales. For example, publishing houses find that children's books are in great demand, so they can take children's books as a theme of the bibliography, make a marketing plan for children's books, and increase sales and market share.

To sum up, the subject of bibliography refers to the subject or subject field enjoyed by a series of books. It provides readers with more choices, and it is also an important means for publishers to conduct market research and book sales.