We present original evidence that abstract and concrete concepts are organized and represented differently, based on statistical analyses of thousands of concepts in publicly available datasets. First, we show that abstract and concrete concepts have differing patterns of association with other concepts. Second, we test recent hypotheses that abstract concepts are organized according to association, whereas concrete concepts are organized according to (semantic) similarity. Third, we present evidence suggesting that concrete representations are more strongly feature-based than abstract representations. We argue that degree of feature- based structure may fundamentally determine concreteness, and discuss implications for cognitive and computational models of meaning.