The Mexican Health and Aging Study (MHAS) is a national longitudinal study of adults aged 50 and over in Mexico. The baseline survey, with national and urban/rural representation of adults born in 1951 or earlier, was conducted in 2001 with follow-up interviews in 2003, 2012, 2015, and 2018. A new sample of adults born between 1952-1962 was added in 2012. Similarly, in 2018, a new cohort of adults born between 1963 and 1968 was added to update the sample. The study is a collaborative effort between researchers from the University of Texas Medical Branch (UTMB), the National Institute of Statistics and Geography (INEGI, Mexico), the University of Wisconsin, the National Institute of Geriatrics (INGER, Mexico), the National Institute of Public Health (INSP, Mexico), and the University of California, Los Angeles (UCLA). The MHAS is partially supported by the National Institutes of Health / National Institute on Aging (R01AG018016, R Wong, PI) and INEGI in Mexico. The overall objective of the study is to examine the aging process and its burden of disease and disability in a large representative panel of older Mexicans, from a wide socioeconomic spectrum. The MHAS design was motivated by several research questions related to the dynamics of health and aging in Mexico; the effect on multiple health domains of health behaviors in early and mid-life, migration, transfers, and socioeconomic status; and health selectivity among migrants to the US and among those returning to Mexico.