One of the most dreaded interview questions is "why do you want to leave your job?" It makes sense that a prospective employer asks that question. First, they want to understand why you are looking to get out of your current job. Second, they want to determine if you pose a hiring risk for their organization. This could indicate that problems may arise after they bring you on board.
When you think about an honest answer to this question, you most likely come up with a negative response. In an interview, you want to be positive and transparent but not divulge all details, just as you would not reveal all of your personal problems in an interview. Here are some typical (honest) responses, and ideas for how to rephrase the answers in your favor.