Are book titles underlined when written?

In formal or academic writing, book titles are usually italicized rather than underlined. For instance:

- *To Kill a Mockingbird* by Harper Lee

- *The Great Gatsby* by F. Scott Fitzgerald

Italicization is the preferred method of emphasis in most style guides, including the MLA, APA, and Chicago styles.

Note: In informal writing or personal communication, it's acceptable to use quotation marks instead of italics to indicate book titles.