The global population of international migrants has grown significantly over the past several decades—from 153 million in 1990 to 272 million in 2019—while the population of international migrants as the share of the world’s total population has remained quite steady. At the same time, the political importance of migration has increased, especially in the US and Western European countries. As a result, studies of immigrant incorporation have become critical for shaping public opinions and informing policymaking. While researchers have explored many facets of migrants’ adaptation and assimilation processes, we still do not fully understand how migration affects their family behavior. This dissertation examines migrant childbearing behavior in West Germany and Turkey, two contexts that have experienced fundamental social change as a result of migration and are also intimately linked by migration. I draw from two data sources, the 1984-2016 German Socio-Economic Panel and the 2013 Turkish Demographic and Health Survey. First, I examine how fertility behavior differs across migrant cohorts in West Germany. I find variation in the patterns of entry into childbearing across arrival cohorts from Turkey and Southern Europe, driven by women’s changing marriage/migration histories. I also find differences at higher parities, including reduced third birth propensities among recent Turkish arrivals, likely a result of changing exposures within origin and destination contexts. Second, I examine contraceptive behavior among internal migrants in Turkey. I find that migration is significantly associated with modern contraceptive use—particularly short-acting contraception—for rural-to urban and urban-to-urban migrants and that this may be explained by the fact that migration, depending on the group, is also associated with changes in economic resources, access to and knowledge of healthcare, mobility and social norms. Third, I look at the impact of urban migration on fertility in Turkey. Results demonstrate that rural-to-urban migrants in urban areas experience accelerated transitions into childbearing, consistent with migration for marriage purposes, despite general adaptation to lower fertility norms. Ultimately, my dissertation deepens our understanding of the complex social processes that underlie migrant fertility behavior.