["Journal of Historical Sociology, Volume 34, Issue 1, Page 161-185, March 2021. ", "\nAbstract\nThis article examines the impact of Mexican eugenics on different programs relating to the family throughout the post‐Revolutionary period. It deals with how Mexican elites thought about the family and how these discussions delimited who should be part of or exist under the banner of “la gran familia mexicana”. I discuss how eugenicists' debates regarding motherhood, puericulture, class, and different preventive health measures were intended to keep “undesirables”—or the people who, in their view, should not be part of “la gran familia mexicana”—at bay. I argue that science was used as a tool for implementing different eugenic plans that would make ideas of mestizaje and “rational mixing” into the modern Mexican nation. I argue that according to the Mexican Society of Eugenics (MSE), it was through the regulation of individual families and the acceptance of eugenic precept of self‐management and rational reproduction that the creation of the national family was to be crafted. Thus, the “gran familia mexicana” would become the organizing principle for both the individual and broader national dynamics in Mexico.\n"]