This article discusses major methodological challenges in the comparative study of the drivers of international mobility (between different times and places) when using household surveys. Noting the difference between the study of coterminous and stage-specific drivers of migration, I highlight the problems of obtaining data with adequate representation across periods and geographies, which are pressing for all social science research but especially for cross-local comparative endeavors. I discuss the advantages and drawbacks of a broad constellation of prospective and retrospective approaches, paying particular attention to the migration ethnosurvey. After briefly describing the general commonalities and differences of ethnosurvey approaches adopted around the world, I suggest how post hoc case selection and other adjustments can help to ameliorate retrospective biases and comparability problems. I conclude with ideas on a priori case selection that can help to bolster comparative migration studies.