Just like there are many questions that an interviewer can ask, there are many that he cannot ask. Some questions are illegal to ask. Many people don't realize that there are off limit questions for employers. When or if you do encounter some of these questions there are ways that you can choose to respond to them. Since some people would probably answer them, it is good to know that you don't have to answer those kinds of questions. You can simply ask how those questions pertain to the job you're applying for.