Measurement of diversity is important in several sciences but has evolved mainly within ecology. An ecological community with many species is more diverse than one with few but the way the total number of individuals is distributed among the species also influences the degree of diversity or heterogeneity. Although not always explicitly used, it can be shown that diversity is a concept of some importance in psychology, too. In general terms quantification of diversity is related to the apportionment of some quantity into a number of well‐defined classes. The dual‐concept type of diversity index reflects both the number of classes and the degree of evenness (homogeneity) of the apportionment. The quantity that is distributed has commonly been a population of elements and apportionment homogeneity measures population heterogeneity. The statistical context has dominated the thinking about the measurement of diversity, heterogeneity, and homogeneity. Some well‐known indices of diversity and the ideas behind them are discussed. It is concluded that the general geometric representation of homogeneity (similarity) and heterogeneity (dissimilarity) (Junge, 1978; 1991) offers a more general approach to the measurement of dive