Purpose: Psychological well-being, an important indicator of successful aging, may be conceptualized quite differently across cultures. Using a mixed-methods approach, we developed a measure of psychological well-being based on the indigenous expertise of Thai elders. Design and Methods: Data were collected from older people in Thailand in four stages with staggered qualitative and quantitative methods: individual and focus group interviews (n = 67); a preliminary survey (n = 477); cognitive interviews (n = 30); and a second survey (n = 460). We analyzed the resulting psychological well-being items to identify their underlying factor structure and psychometric properties. Results: Confirmatory factor analysis suggested that psychological well-being has two components: intrapersonal and interpersonal. The subscales for this measure have adequate reliability and validity. Implications: This research provides evidence for cultural variability in the nature of psychological well-being and highlights the importance of developing measures that are culturally relevant.Key Words: Successful aging, Measurement, Culture, Asian elders