Italics are typically used to show emphasis or to denote titles of stand-alone works. Different style guides have different rules about what to italicize. Here are some good general guidelines, but the most important thing is to stay consistent within your work.
Titles of Works
In most cases, you should italicize the titles of complete works, like books or movies. Some style guides, like APA format, prefer underlining titles. MLA format prefers italics. If you aren’t using a particular style guide, it’s really up to you. Just know that a title shouldn’t have both italics and underlining.
You should generally italicize titles of novels, like The Great Gatsby, Beloved, and The Catcher in the Rye. You would also italicize the names of feature-length films, like Rocky, Schindler’s List, and Frozen. Music albums, TV shows, and names of newspapers and magazines should also be italicized because they’re singular works.
On the other hand, shorter works (like short stories, poems, individual songs, short films, and individual TV episodes) usually use quotation marks. This shows that they’re parts of larger works. If you can’t remember whether to use italics or quotation marks, try asking yourself if you’d be able to buy the title at the store by itself. If not, then it should probably get quotation marks. For example, you could say: “The first story in David Sedaris’ debut short story collection, Me Talk Pretty One Day, is called ‘Go Carolina.'”
As always, there are some exceptions. Complete religious works aren’t italicized or underlined. For example, the Bible, the Koran, and the Torah are all capitalized, but not otherwise signified. In addition, specific books within the religious works (like the book of Genesis) don’t receive italics, underlining, or quotation marks.
When a punctuation mark is part of the work’s title, you should italicize it. One example is Judy Blume’s book Are You There, God? It’s Me, Margaret. If a punctuation mark after the title isn’t part of the title, it shouldn’t be italicized. For example: “Have you ever read The Hitchhiker’s Guide to the Galaxy?” Here, the question mark isn’t italicized because it’s not part of the book’s title.
Names of Ships and Aircraft
The proper names of ships, vessels, and aircraft should be italicized. For example, the Titanic, Apollo 11 and the U.S.S. Hornet are all italicized. Notice that “U.S.S.” isn’t italicized, because it isn’t part of the proper name.
Italics can also emphasize a single word or phrase. For example: “I don’t care what he thinks. I do what I want!” It’s best to use italics for emphasis sparingly so that they retain their impact.
When you’re referring to words as nouns or objects, you should also use italics to help offset it from the rest of the sentence. For example: “The word anxious has a different connotation than the word worried.”
Foreign words that haven’t fully been adopted by English tend to be italicized. For example: “Lee waved goodbye to his halmeoni from the bus window.” Foreign words that are commonly used in English, like bon voyage or alma mater, don’t necessarily need italics in a sentence. For example, “She wished him bon voyage when she dropped him off at the airport.”
Onomatopoeic words (or words that sound like sounds) are usually italicized, as well. For example: “The book landed on the floor with a hearty thwack!” In this case, if an exclamation point is used, it should also be italicized.
The exact rules for using italics depend on the specific style guide you’re using. If you’re not following a style guide, these guidelines are a safe bet. The most important rule is to be consistent.