Inequality and concentration are central concepts in all the social sciences. Economists study inequalities in the distribution of wealth, income, productivity, or goods. Sociologists may be concerned with social mobility-inequality of opportunity-or with inequalities in living conditions-the degree to which minority groups are concentrated in particular residential areas. A political scientist must be concerned with political inequality-concentrated, unequally distributed power. He may, for instance, need a measure of legislative malapportionment. Though the variables may be different, the basic question is the same: What is the degree to which wealth, or good living conditions, or power, are concentrated in a society? Since the questions are conceptually similar, it is reasonable to expect that the problems of quantification might be similar, and that the tools of measurement developed in one social science might be applicable to studies in another field. Yet there has been little interchange across disciplines, and scholars in each field persist in using techniques which are in some respects inferior to those used other fields. This article examines a number of measures of inequality, evaluates their strengths and weaknesses, and compares the results given by some of the measures when they were applied to data on representation state legislatures and on land distribution.