The appearance of this volume attests to the growing interest in humanness and dehumanization among psychologists. That growth has been luxuriant: One scientific database reveals that the past 5 years (2007-2011) have generated more psychology articles mentioning dehumanization than were published in the preceding 40. With this increase has come a proliferation of conceptual approaches, methodologies, and stated or unstated working definitions of dehumanization and related concepts. In this chapter, I attempt to impose some order on this diversity and in the process try to get closer to a clear understanding of these fascinating ideas.