Taken from Ask.com
We use italics (characters set in type that slants to the right) and underlining to distinguish certain words from others within the text. These typographical devices mean the same thing; therefore, it would be unusual to use both within the same text and it would certainly be unwise to italicize an underlined word. As word-processors and printers become more sophisticated and their published products more professional looking, italics are accepted by more and more instructors. Still, some instructors insist on underlines (probably because they went to school when italics were either technically difficult or practically unreadable). It is still a good idea to ask your instructor before using italics. (The APA Publication Manual continues to insist on underlining.) In this section, we will use italics only, but they should be considered interchangeable with underlined text.
These rules and suggestions do not apply to newspaper writing, which has its own set of regulations in this matter.
Italics do not include punctuation marks (end marks or parentheses, for instance) next to the words being italicized unless those punctuation marks are meant to be considered as part of what is being italicized: “Have you read Stephen King’s Pet Semetary? (The question mark is not italicize here.) Also, do not italicize the apostrophe-s which creates the possessive of a title: “What is the Courant ‘s position on this issue?” You’ll have to watch your word-processor on this, as most word-processors will try to italicize the entire word that you double-click on.
Generally, we italicize the titles of things that can stand by themselves. Thus we differentiate between the titles of novels and journals, say, and the titles of poems, short stories, articles, and episodes (for television shows). The titles of these shorter pieces would be surrounded with double quotation marks.
In writing the titles of newspapers, do not italicize the word the, even when it is part of the title (the New York Times), and do not italicize the name of the city in which the newspaper is published unless that name is part of the title: the Hartford Courant, but the London Times.
Other titles that we would italicize include the following:
Journals and Magazines: Time, U.S. News and World Report, Crazyhorse, Georgia Review
Plays: Waiting for Godot, Long Day’s Journey Into Night
Long Musical Pieces: Puccini’s Madama Butterfly, Tchaikovsky’s Nutcracker Suite (but “Waltz of the Flowers”), Schubert’s Winterreise (but “Ave Maria”). For musical pieces named by type, number and key — Mozart’s Divertimento in D major, Barber’s Cello Sonata Op. 6 — we use neither italics nor quotation marks.
Cinema: Slingblade, Shine, The Invisible Man
Television and Radio Programs: Dateline, Seinfeld, Fresh Air, Car Talk
Artworks: the Venus de Milo, Whistler’s The Artist’s Mother
Famous Speeches: Lincoln’s Gettysburg Address, Washington’s Second Inaugural Address (when that is the actual title of the speech)
Long Poems (that are extensive enough to appear in a book by themselves): Longfellow’s Evangeline, Milton’s Paradise Lost, Whitman’s Leaves of Grass
Pamphlets: New Developments in AIDS Research
We do not italicize the titles of long sacred works: the Bible, the Koran. Nor do we italicize the titles of books of the Bible: Genesis, Revelation, 1 Corinthians.
When an exclamation mark or question mark is part of a title, make sure that that mark is italicized along with the title,
My favorite book is Where Have All the Flowers Gone?
I love Dr. Seuss’s Oh, the Places You’ll Go!
(Do not add an additional period to end such sentences.) If the end mark is not part of the title, but is added to indicate a question or exclamation, do not italicize that mark.
Did you enjoy Charles Frazier’s Cold Mountain?
Names of Vehicles
U.S.S. Eisenhower (Don’t italicize the U.S.S.)
H.M.S. Pinafore (Don’t italicize the H.M.S. when you’re talking about the ship. If you’re talking about the light opera, then it’s part of the title, H.M.S. Pinafore.)
We don’t italicize names of vehicles that are brand names: Ford Explorer, Corvette, Nissan Pathfinder, Boeing 747.
Foreign Words or Phrases
If a word or phrase has become so widely used and understood that it has become part of the English language — such as the French “bon voyage” or the abbreviation for the latin et cetera, “etc.” — we would not italicize it. Often this becomes a matter of private judgment and context. For instance, whether you italicize the Italian sotto voce depends largely on your audience and your subject matter.
Words as Words
The word basically is often unnecessary and should be removed.
There were four and’s and one therefore in that last sentence. (Notice that the apostrophe-s, used to create the plural of the word-as-word and, is not italicized. See the section on Plurals for additional help.)
She defines ambiguity in a positive way, as the ability of a word to mean more than one thing at the same time.
Note: It is important not to overdo the use of italics to emphasize words. After a while, it loses its effect and the language starts to sound like something out of a comic book.
I really don’t care what you think! (Notice that just about any word in that sentence could have been italicized, depending on how the person said the sentence.)
These rules do not apply to newspaper writing.
Words as Reproduced Sounds
Grrr! went the bear. (But you would say “the bear growled” because growled reports the nature of the sound but doesn’t try to reproduce it. Thus the bees buzz but go bzzzz and dogs bark woof!)
His head hit the stairs, kathunk!
Frequently, mimetically produced sounds are also accompanied by exclamation marks.