The transition from financial dependence on one's parents to financial self-sufficiency is one of the most relevant transitions during emerging adulthood. It is important to have an instrument able to assess emerging adults' financial capabilities and to detect its change over time. The current article aims to collect international evidence of the Financial Identity Scale (FIS) validity and reliability. Cross-sectional data collected from 2,501 emerging adults aged 18--25 and belonging to three different countries--U.S. (n = 1,535), Italy (n = 485), and Lithuania (n = 481)--were adopted to test score structure validity, generalizability, sensitivity to difference, criterion-related validity, and internal consistency. Instead, four-wave longitudinal data, available for the American sample only (n = 1,900), were adopted to test FIS structural stability and sensitivity to change. As recommended by the contemporary view of validity, different structural equation models were performed. Findings suggest that FIS scores are valid and reliable. The implications for researchers and practitioners are discussed.