This dissertation advances our understanding of the assimilation processes of post-1965 immigrants and their descendants. In particular, I select issues that have not been intensively examined before, addressing three major life events during adulthood, including college education, union formation, and labor market outcomes, to investigate adaptation processes of immigrants and their offspring. Chapter 2 examines the possible educational pathways the new second immigrant generation may take during transition to adulthood. To assess their degree of assimilation, I make two levels of comparison. At the first level, I examine horizontal intergenerational mobility by comparing the educational status of the new second generation with their parents. I find that the new second-generation youth, as a whole, are doing better than their parents in high school graduation. However, the pace and degree of intergenerational mobility varies by ethnic backgrounds regarding college education. At the second level, I assess vertical inter-class mobility by comparing the educational status of the new second generation with the third- and higher-generation non-Hispanic white peers (mainstream proxy). I find that there is stratification of college education for interclass mobility. While Mexican Americans are much less likely to attend college than their third- and higher-generation white counterparts, Cuban Americans and Asian Americans are more likely to go on with college education than their third- and plus-generation non-Hispanic white generation. Disadvantaged groups, like Mexican Americans and those of other Central-South American and Caribbean origins, lag behind in such social factors as parental human capital, family structure, and family size, which contribute to reduce their likelihood of college education and probably their eventual lower status in American stratification system. Chapter 3 examines union formation processes among young adults of different immigrant generations during transition to adulthood. As living together without marrying becomes a common phenomenon among young adults in American society, one may ask whether immigrant descendants who are raised in ethnic Asian or Hispanic families will take the union formation pattern of cohabitation as their native peers do. This chapter provides strong and robust evidence regarding that first generation youth are less likely to embrace the alternative union formation path of cohabitation in the presence of cultural, structural, and contextual controls, as compared to the third and higher-generation non-Hispanic white peers. In addition, the first generation is more likely to take the traditional route of marriage during early adulthood. Chapter 4 shifts the research attention to examine the economic adaptation processes of contemporary Asian and Hispanic immigrants in comparison to their native peers in the context of a segmented labor market. I first re-define the U.S. labor market into four segments: non-enclave primary segment, non-enclave secondary segment, enclave-primary segment, and enclave-secondary segment. I then focus on the impact of various nativity and immigrant statuses on labor market outcomes, including labor segment membership, hourly wages, and non-monetary job benefits, among immigrants. I find that native-born and naturalized citizenship are more advantageous statuses than non-permanent residency and permanent residency to incorporate immigrants and their descendants into the mainstream labor market and facilitate their attainment of higher wages and more job benefits. Non-naturalized immigrants are much more likely to be concentrated in ethnic enclaves and in lower rungs of the open market, and subject to lower pay and fewer benefits due to their inferior immigrant statuses.