A book review is a form of literary criticism in which a book is merely described (summary review) or analyzed based on content, style, and merit. A book review may be a primary source, opinion piece, summary review or scholarly review. Books can be reviewed for printed periodicals, magazines and newspapers, as school work, or for book web sites on the Internet. A book review's length may vary from a single paragraph to a substantial essay. Such a review may evaluate the book on the basis of personal taste. Reviewers may use the occasion of a book review for an extended essay that can be closely or loosely related to the subject of the book, or to promulgate their own ideas on the topic of a fiction or non-fiction work.
Some journals are devoted to book reviews, and reviews are indexed in databases such as Book Review Index and Kirkus Reviews; but many more book reviews can be found in newspaper and scholarly databases such as Arts and Humanities Citation Index, Social Sciences Citation Index and discipline-specific databases.
Photios I of Constantinople has been called "the inventor of the book-review" for his work, Bibliotheca.