This article reviews the demographic sources available in Spain for the study of internal migration. We outline the differences between each of these sources and compare how each source tracks internal migration in terms of annual evolution, measured by decade since 1960, and in recent times. These comparisons allow us to check both the constancy and incongruities between the different sources. We find that the most consistent results are obtained from the Census Data and the Encuesta Sociodemografica (Sociodemographic Survey). The Encuesta de Migraciones (Migrations Survey) and the Estadisticas de Variaciones Residenciales (Residential Change Statistics) are less reliable. The problems with the last two sources are associated with the management of the Padron de Habitantes (local population register), which alters the sampling for the Encuesta de Migraciones and the accurate registration of additions and withdrawals for the Estadisticas de Variaciones Residenciales. To improve the results of these sources, it is necessary to impute a crucial task on the management of the Padron: to ensure that the register accurately corresponds to the real residential situation of the population. We argue that studies must pay closer attention to the suitability of each source in relation to their object of research and its objectives. But in many studies such deeper reflection is lacking.
