In a job interview, it's easy to feel powerless.
Interviews, and the people who conduct them, can be exceptionally intimidating. You're nervous, and the person questioning you has the power to give or deny you access to something that you want badly, something that could change your life. It is, therefore, understandable if you feel compelled to answer any question posed to you during the interview.
The truth, however, is more complicated.
Interviewers cannot simply ask about any subject they choose, and you don't have answer the questions or parts of questions that are illegal. Some subjects are almost always illegal for interviewers to touch upon, and doing so could open them, and the companies they represent, up to liability for employment discrimination in a lawsuit.
You can, of course, choose to answer such queries if you feel comfortable doing so. However, if the interviewer continues to pursue an illegal topic and you begin to feel uncomfortable, you don't have to continue answering.
Let's take a look at some illegal interview questions and ways to respond to them.