You can usually divide job interview questions into four categories, based on the kinds of answers you're trying to elicit.

Closed-ended
Definition: Questions that call for a simple, informational answer – usually a yes or no.
Examples:

• "How many years did you work for the circus?"
• "Did you enjoy it?"
• "What cities did you tour?"

When to use them: Closed-ended questions work best if you're trying to elicit specific information or set the stage for more complex questions.
Pitfall to avoid: Asking too many of them in rapid-fire succession and failing to tie them back to the job criteria, thus making candidates feel as though they're being interrogated.

Open-ended
Definition: Questions that require thought and oblige the candidate to reveal attitudes or opinions.
Examples:

• "Describe for me how you handle stress on the job."
• "Can you give me an example of how you improved productivity at your last job?"

When to use them: Most of the time, but interspersed with closed-ended questions. Using open-ended questions related to candidates' past experiences on the job is known as behavioral interviewing. Because this approach requires candidates to describe how they've handled real tasks and problems, it can be very useful and revealing.
Pitfalls to avoid: Not being specific enough as you phrase the question and not interceding if the candidate's answer starts to veer off track.

Hypothetical
Definition: Questions that invite the candidate to resolve an imaginary situation or react to a given situation.
Examples:

• "If you were the purchasing manager, would you institute an automated purchase-order system?"
• "If you were to take over this department, what's the first thing you'd do to improve productivity?"

When to use them: Useful if framed in the context of actual job situations.
Pitfall to avoid: Putting too much stock in the candidate's hypothetical answer. (You're usually better off asking questions that force a candidate to use an actual experience as the basis for an answer.)

Leading
Definition: Questions asked in such a way that the answer you're looking for is obvious.
Examples:

• "You rarely fought with your last boss, right?"
• "You know a lot about team-building, don't you?"
• "You wouldn't dream of falsifying your expense accounts, would you?"

When to use them: Rarely, if ever. You're not likely to get an honest answer – just the answer you want to hear. And you run the risk of appearing unprofessional.