The goals of the studies reported in this dissertation were to expand on the measurement of Bicultural Identity Integration (BII) and to test BII theory in an ethnically diverse sample of bicultural individuals from different generational groups. BII is an individual difference construct that captures variations in the structure and experience of biculturalism (Benet-Martínez & Haritatos, 2005). In 3 studies, I examined BII using qualitative methods (Study 1) and wrote new BII items based on these qualitative data, examined the quality of the new measure (Bicultural Identity Integration Scale--Version 2 or BIIS-2) using subject-matter experts (Study 2a) and college students (Study 2b), and then collected validation data from bicultural college students (N = 1049) at a large, public university on the West Coast (Study 3). Results showed that the BIIS-2 yields reliable (.81 < α < .86) and stable (n = 240; M = 6.93 days, SD = 0.90 days; Time 1 and Time 2 correlations: .74 < r < .78) scores. I used exploratory factor analyses to select items and establish the factor structure of the BIIS-2 with a random subset of the large sample (n = 600), confirmatory factor analyses to show that the factor structure fit the data well (n = 449), and multi-group confirmatory factor analyses to show measurement invariance in two ethnic groups and two generational groups. The data also revealed interesting and important patterns of correlates. Specifically, there were significant and meaningful correlations with personality traits, acculturative stress, and psychological well-being. In addition, path analyses confirmed that in general, personality and acculturation variables influence individuals' perceptions about their dual identities (BII), which in turn influences adjustment, but there were interesting and important generational differences on how these variables are related. These findings lend support for the construct validity of BII, add to our understanding of the social, personality, and adjustment correlates of the bicultural experience, and have important implications for the well-being of bicultural individuals.