Though natural language processing has come far in the past twenty years, the technology has not achieved a major impact on society. Is this because of some fundamental limitation that cannot be overcome? Or because there has not been enough time to refine and apply theoretical work already done? Editors Madeleine Bates and Ralph Weischedel believe it is neither; they feel that several critical issues have never been adequately addressed in either theoretical or applied work, and they have invited capable researchers in the field to do that in Challenges in Natural Language Processing.