This paper investigates the measurement of developmental idealism. Developmental idealism is a set of beliefs and values stating that modern societies and families are better than traditional ones, that modern families facilitate modern societies, and that modern societies foster modern families. Prior research has shown that developmental idealism is widespread globally but has provided little evidence about whether beliefs concerning developmental idealism can be measured reliably at the individual level. It also has provided little information about the dimensionality and psychometric properties of measures of developmental idealism. Using cross-sectional survey data from Argentina, China, and Egypt, we explore and test the factor structure underlying observed measures for aspects of developmental idealism and estimate the reliability of different models. Theory and data suggest that developmental idealism consists of multiple dimensions, and when family-related items are measuring similar underlying constructs, the measurement reliabilities are high. These results provide evidence that the dimensions of developmental idealism can be measured with a high degree of reliability.