Most of us possess the intuitive feeling that abstract word concepts are harder to understand than concrete word concepts. If you ask people why this is do, their answer would most likely reflect the belief that abstract words are hard to understand because they lack the fairly direct sensory referents that concrete words have. In fact, in cognitive psychology, it has long been assumed that it is this difference between these two concept types that makes abstract concepts harder to understand, process, acquire, remember, and so on than concrete ones. In this chapter, I use concreteness as a generic term to refer generally to the constellation of variables that distinguish abstract words from concrete words. However, the term is used merely as a convenience for differentiating among word types and, by itself, should not be taken to imply that abstract words are harder to understand than concrete words because they lack direct sensory referents. Instead, my purpose here is to evaluate that basic explanation.