With this question, your interviewer is looking for two things. First, how impressive are the greatest hits of your career so far? Second, what do you value? Naturally, you want to choose an accomplishment that demonstrates your talents/strengths/smarts. At the same time, remember that your answer also shows what kind of achievements you value most. If you believe your greatest accomplishment is winning a prestigious sales award, it shows that you're someone who is driven and cares about helping the company succeed. If you believe your greatest accomplishment is spending a month in India building schools, that shows you are someone who is driven and civic-minded and cares about helping people. Both of the above are good answers, but say different things about the candidate. Do what you can to illustrate how your greatest accomplishment shows strengths that will be relevant for the job at hand. For maximum impact, you may want to use the Big Interview Answer Builder to help you hone your description of your greatest professional accomplishment.