This chapter describes some of the measurement tools that can be used in the quantitative analysis of inequality. It introduces some quantitative methods used to discover and assess inequalities among population groups in multiple dimensions, typically described by categorical variables. Inequality refers to the unequal distribution of socially relevant resources among individuals or groups in society. Simple inequality measures originate from the statistical concept of variability of a distribution. All the measures are zero when all incomes are equal and increase with inequality. A systematic approach to inequality measurement is to start with a Social Welfare Function (SWF) that encompasses specific ethical principles, and to derive an inequality index from it that reflects these same properties. Inequality, however, can have several dimensions: non-income inequality includes inequality in skills, education, opportunities, health, and others. Relationships between inequality in income and non-income dimensions are of great interest.