Migratory workers, particularly migratory farm workers, engage in a type of migration which is temporary, often repetitive, following a seasonal course during the year. This type of migration needs to be conceptually more clearly distinguished from other types of internal and international migration which more or less permanently redistribute population. A fuller exploration of the problems of defining migratory workers is needed at both the conceptual level and at the level at which the concepts are translated into workable survey definitions. The dynamic and causal factors underlying migratoriness probably differ greatly from those underlying the general phenomenon of internal migration. Thus while the volume of internal migration is positively correlated with changes in the business cycle, the volume of migratoriness appears to change in counter-cyclical fashion. Information is presented on the number of domestic and foreign migratory farm workers in the United States in 1950 and on the composition, the martial status, and on the number of children under 18 of domestic migratory farm workers.