The title of a book should be capitalized when written in a sentence. Additional formatting, such as quotation marks or underlining, depends on the overall style expectations for the paper.
When indicating a book title in a sentence, writers should capitalize each word of the title. However, it is important to consult the instructor, publication, or general style guide for the work being written since there may be other formatting requirements. For example, the American Psychological Association format requires that titles be capitalized and italicized. Some courses or publications may have their own style guide that indicate underlining is also an appropriate way to identify a title in a sentence.