Project Abstract There exists a shortage of knowledge about how the health of US Mexican immigrants, a population of 12.3 million, is impacted by circular immigration patterns. This population is highly vulnerable to health risks and stress arising from poverty, discrimination, cultural differences, and immigration policy enforcement. Addressing this from a public health perspective requires an understanding of the conditions under which immigrant populations are exposed to health risks in their country of origin, while migrating, at their destination context or upon returning to their home country. The proposed international research collaboration has the potential to build a solid research foundation for developing interventions to achieve health equity for an underserved minority population of US immigrants. The research proposed aims to address this knowledge gap by examining the mechanisms by which immigration processes expose individuals to distinct environments, increases susceptibility to risk behaviors and contributes to mental and physical health disparities, infectious diseases and alcohol/drug dependence in the host or origin communities. Using the Symbiotic Model of Risk Reduction, this study proposes a concurrent mixed-methods nested design to recruit a sample of 600 that will include two subgroups of floating recent immigrants (within the past 5 years) that have arrived to Los Angeles and a group who have returned to Mexico City either voluntary or forced. The specific aims will: 1) Determine the prevalence of physical health (cardiovascular, metabolic dysregulation), mental health, infection, and substance abuse/dependence outcomes; 2) Identify and characterize the association between migration histories and health outcomes for the subgroups of floating populations; 3) Determine whether individual, social and environmental determinants mediate and/or moderate the relationships among the migration subgroups and varying health condition outcomes; 4) Characterize qualitatively the influence of culture and community context on strategies, practices and circumstances for maintaining safer (or riskier) health status and substance use.