If someone were to put together a list of the most hated interview questions, there is little doubt that one of the top ten would be “Why are you applying for this position?” The short and glib answer would be simply that I want the money. That is also the answer that no one should ever give. If you have done even a brief amount of homework on the company before you sent your resume, then you should know enough to answer this question.
If you have been out of work for any length of time, a somewhat honest answer is a good idea. Tell the interviewer that you have been waiting for a position such as this to open up. Go into detail of what you offer the company at this specific time and for this specific job. Interviewing is about generalities on their end and specifics on yours. You need for them to see you as someone ready to get started the moment you are hired.
If you are currently employed, you are in a better position. Tell the interviewer that you have been waiting for this position to open and then tell them why. Again, go into detail about what you offer.
One thing to be cautious of is if the interviewer words the question in a way to elicit information about your current or previous employer. This is about integrity, and it is common for the interviewer to see if you are the sort of person that is going to bad mouth your employer. That is never a good idea. Make it clear that you aren’t unhappy with your current job but that you would enjoy the one you are applying for even more. You want to leave the interviewer with a positive image of you.