What part of bibliographic reference is always italicized or underlined?

The title of a book, journal, or other independent publication is always italicized or underlined in a bibliographic reference.

For example:

* Book: _The Lord of the Rings_ by J.R.R. Tolkien

* Journal: _Nature_

* Newspaper: _The New York Times_

Note: The title of an article or chapter within a larger work is put in quotation marks, not italicized or underlined.