Use a question mark [ ? ] at the end of a direct question. It is considered bad form to use a question mark in combination with other marks, although that is often done in informal prose in an attempt to convey complex tones: He told you what!? That combination (or similar combination) of punctuation marks is sometimes called an interrobang, but the interrobang currently has no role in academic prose.*
A tag question is a device used to turn a statement into a question. It nearly always consists of a pronoun, a helping verb, and sometimes the word not. Although it begins as a statement, the tag question prevails when it comes to the end-mark: use a question mark. Notice that when the statement is positive, the tag question is expressed in the negative; when the statement is negative, the tag question is positive. (There are a few exceptions to this, frequently expressing an element of surprise or sarcasm: "So you've made your first million, have you?" "Oh, that's your plan, is it?") The following are more typical tag questions:
Be careful not to put a question mark at the end of an indirect question.
Be careful to distinguish between an indirect question (above), and a question that is embedded within a statement which we do want to end with a question mark.
Put a question mark at the end of a sentence that is, in fact, a direct question. (Sometimes writers will simply forget.) Rhetorical questions (asked when an answer is not really expected), by the way, are questions and deserve to end with a question mark:
Sometimes a question will actually end with a series of brief questions. When that happens, especially when the brief questions are more or less follow-up questions to the main question, each of the little questions can begin with a lowercase letter and end with a question mark.
If a question mark is part of an italicized or underlined title, make sure that the question mark is also italicized:
(Do not add a period after such a sentence that ends with the title's question mark. The question mark will also suffice to end the sentence.) If the question mark is not part of a sentence-ending title, don't italicize the question mark:
When a question ends with an abbreviation, end the abbreviation with a period and then add the question mark.
When a question constitutes a polite request, it is usually not followed by a question mark. This becomes more true as the request becomes longer and more complex:
The Interrobang*In case you're interested in the interrobang, you should know that you're in good and serious company. Some people think it ought to look like the symbol to the right of this paragraph. Click on the interrobang to visit a Web site devoted to its care and feeding.