The process of urbanization of peasant migrants in a developing country is the methodological and theoretical focus of this study. More specifically, this involves a follow-up case study in depth of out- migrants from the small peasant community of Aldea San Francisco, Entre Rios, Argentina, the causes and effects of migration upon origin and destination, and the problems of assimilation, giving special attention to changes in attitudes and behavior. In attempting to achieve this level of understanding, three major objectives are proposed: First, to study attitudes, decisions and behavior relating to migration of the various population subgroups and their eventual assimilation or non- assimilation into new environments; second, to develop an understanding of the interrelationship of psychosocial, spatial, environmental, economic and other factors that lead to or impel migration by different social classes; and third, to explore the general implications of migration and urban assimilation upon rural and urban development. This data, a complete history of a migrant population from rural origin to assimilation in new environments, provides an instance for documenting the entire migration process.