Use an exclamation point [ ! ] at the end of an emphatic declaration, interjection, or command.
"No!" he yelled. "Do it now!"
An exclamation mark may be used to close questions that are meant to convey extreme emotion, as in
What on earth are you doing! Stop!
An exclamation mark can be inserted within parentheses to emphasize a word within a sentence.
We have some really(!) low-priced rugs on sale this week.
Note that there is no space between the last letter of the word so emphasized and the parentheses. This device should be used rarely, if ever, in formal text.
An exclamation mark will often accompany mimetically produced sounds, as in
"All night long, the dogs woof! in my neighbor's yard" and
"The bear went Grr!, and I went left."
If an exclamation mark is part of an italicized or underlined title, make sure that the exclamation mark is also italicized or underlined:
My favorite book is Oh, the Places You'll Go!
(Do not add a period after such a sentence that ends with the title's exclamation mark. The exclamation mark will also suffice to end the sentence.) If the exclamation mark is not part of a sentence-ending title, don't italicize the exclamation mark:
I've asked you not to sing la Marseillaise!
In academic prose, an exclamation point is used rarely, if at all, and in newspaper writing the exclamation point is virtually nonexistent.