This thesis investigates the development of proto-eugenic thought and policy in Porfirian Mexico and how those ideas were important to the Mexican eugenics movement of the twentieth-century. Proto-eugenics is the name given to the ideas of biological and racial improvement developed by leading Mexican thinkers in the late nineteenth-century, until the Mexican Revolution of 1910. Proto-eugenic thought was most concerned with eliminating immoral and degenerate traits that could be passed down from parent to child, and encouraging those with prized traits to have children. Through discussion of writings on criminality and education, this thesis argues that proto-eugenic thought had a large influence on the development of Mexican eugenics in the twentieth-century, and the importance of proto-eugenic thought on nationalism in the Porfiriato. It is important to understand how proto-eugenic science was created in order to investigate the development of eugenic social policy in the twentieth-century.